Ernie, I think picton has it.
Oh and please can we not call it tactical voting.
It’s taking your single vote, your one and only, and transferring it to the candidate that you think is the best balance of who you would you would like to win against who is likely to win.
A manual version of the automated Single Transferable Vote system – one of a number of electoral systems loosely and inaccurately termed proportional representation, even though STV is arguably Aldo still a form of FTP. (Though it is certainly more proportional than bloody minded tribal-FTP voting)
This is exactly the sort of thing the LibDems in particular have been openly campaigning for for years, though admittedly I think they’d prefer a more formal and automated version.
PS – nothing dishonest in tactical voting.
Honourable I would suggest
If you want say Labour most, LibDem you could accept and preferably not the Tories, but the local opinion polls are suggesting Tories probably, LibDems possibly and Labour no chance (and variations on that are played out all over the country) the honourable thing to do is vote LibDem as the closest likely winner to the one you want.
You can’t always get what you want, but if you try sometimes, you just might find, you get what you need.