Probably Frank, I said I couldn’t spell it! TBF I’ve only ever heard it said, I don’t think I’ve seen it written down anywhere.
.
I think there might be two conversations going on here? I think the OP was asking about words which only crop in a single context, in my example to prorouge parliament, I can’t think of anything else which can be prorouged. Yes, elephant only means one thing, but it’s never only used in one context (like petard, you are only ever hoisted by it, nothing else ever gets done with a petard)

clouds scudding across the sky

“No they don’t, trying to be smart and looking stupid there.
Elephant herd wandering across the plains.
Let’s address the elephant in the room..”

Looking Stoopider…

“No they don’t, trying to be smart and looking stupid there.
Elephant herd wandering across the plains.
Let’s address the elephant in the room..”

Looking Stoopider…

First you have to notice it.

Plenty of swear words are single use.

Pétard is alive and well in French. It’s a hand gun, spliff, and a banger amongst other things. If you’re en pétard you’re angry and it’s your arse rather than a fart, that’s pet which gives us the verb péter and so on…

How about words that have no opposite version. vis

disconsolate, dejected, disgruntled. Incorrigible, disarray

one cannot be consolate, jected, or gruntled – although I’m not even sure that sounds better anyway. Nor can you be corridged although I guess you can array…

“I could see that, if not actually disgruntled, he was far from being gruntled.” 
P G Woodehouse

tenterhooks

The one thats gets me is flammable and inflammable mean the same.

I love archaic words

Champing can be used as a synonym for chewing vigorously. “He was champing on a mars bar”

incorrigible has an opposite, corrigible.

I was pondering ‘luke’ as in ‘luke warm’. Peculiar in that it seems to only describe temperature and  liquids – you wouldn’t describe air or a solid as luke warm – and you don’t use ‘luke’ to quantify anything else – a lamp that is luke bright, an object that luke heavy.

Further more its a temperature of liquid that is typically undesirable – so luke warm can be both too hot and too cold – you wouldn’t be happy if either your lager or your soup were served luke wam but you wouldn’t expect luke warm lager and luke warm soup to be the same temperature – so its not a particular temperature – its a disappointing or underwhelming temperature.

The one thats gets me is flammable and inflammable mean the same.

They actually don’t – the ‘in’ is an intensifier in many cases rather than ‘opposite of’- such as in ‘intense’ so it means ‘more flammable’ not ‘unflammable’

Flammable means something that can be set on fire – materials that are flammable are ones that  if you put a match to them they’d eventually burn

Inflammable is an unstable material with very low ingition temperature or that can catch fire very easily or even spontaneously. Inflammable material could be ingniteted by a spark, or by percussion – diesel vapour in an engine is ignited just by compressing it

So wood is flammable, petrol is inflammable.

Corrigendum.

A fossil word is a word that is broadly obsolete but remains in current use due to its presence within an idiom, word sense, or phrase.[1][2] An example for a word sense is ‘navy’ in ‘merchant navy’, which means ‘commercial fleet’ (although that sense of navy is obsolete elsewhere). “

Is this why we end up with members of Parliament referred to as “honourable friend/member/gentleman” that somewhere in the distant past honourable had a wholly different meaning that it no longer does?

So wood is flammable, petrol is inflammable.

Beat me to it.

disconsolate, dejected, disgruntled. Incorrigible, disarray

one cannot be consolate, jected, or gruntled

Disgruntled is the same. Dis- is an intensifier, it means very gruntled.

I was pondering ‘luke’ as in ‘luke warm’.

Is lukewarm not one word?

(It’s also the internal temperature of a Tauntaun.)

Dis- is an intensifier, it means very gruntled.

So is the “re” in refried beans. They are only fried once, but very intensely.

I did not know that.

Aside –

So wood is flammable, petrol is inflammable.

Technically, wood is combustible and petrol is flammable, considering the flash point of these substances.

My MIL refers to things being ‘couth’ or ‘not very couth.’

Double post

One use phrase 🙂

So is the “re” in refried beans. They are only fried once, but very intensely.

Refried in that context is a mistranslation of refrito which really means re-hash or re-do, When you cook refried beans you don’t really fry them at all – theres oil in the recipe but the stuff is basically mash.The beans are being cooked for the second time as you start with beans that are already cooked.

while looking up some of those words I discovered the the reason you can’t be ‘jected’ (as in dejected) is because the root word jacere is Latin for thrown and de means down, so down-thrown.

English is both weird and cool.

disarray

Items can be in perfect array. Array being order and disarray disorder.

Now that incandescent light bulbs are a thing of the past, ‘incandescent with rage’ could become one of your single use words.

Yeah ‘Compact Fluorescent with Rage’ describes a very different kind of anger 🙂

Items can be in perfect array. Array being order and disarray disorder.

Yes of course, I even said so.

Couth, kempt and shevelled.

mallemaroking: the drunken carousing of icebound sailors.

I don’t often get to use it much these days thanks to climate change.

One of my favourite words which always worth dropping into conversation is discombobulated. Helped I think by the fact that one is never combobulated.

clouds scudding across the sky

Planing dinghies scud across the waves.

scud1 /skud/
intransitive verb (scuddˈing; scuddˈed)
(esp of clouds) to sweep along easily and swiftly
(esp of sailing vessels) to drive before the wind
transitive verb
To cross swiftly
noun
An act or the action of scudding
Driving cloud, shower or spray
A gust
A swift runner (school sl)
ORIGIN: Perh alteration of scut rabbit’s tail, hence meaning ‘to run like a rabbit’

I thought we got scudding done in desert storm?

Do you tribulations without trials?

tenterhooks

Well there is the saying and the device being used for its intended purpose so you could argue there are two uses for the word.

Morning ablutions

One of my favourite words which always worth dropping into conversation is discombobulated

May I wish you sir, my enthusiastic contrafibularities on the success of your work.

elephant only means one thing, but it’s never only used in one context

I remember in the 60s being disappointed when mom said we were going to the village fate to see the White Elephant Stall .

Kiley (bit in the end of the hammer)

Quirk (glove part)

Forges (glove part)

Extols the virtues of

Most of us own aglets.
How seldom we praise those lifestyle essentials.

Anyways I need to attach a hatband to my Tarphat, now where did I place my etui?

TBH I use aglet and etui more than I should but only because certain crossword compilers find them useful.