presque vu

I think that comes from a passage in Catch 22 and means 'almost seen' in French. When you think you've seen something (almost) but haven't.

As for the other question, some linguists preferred linguistician for a student of linguistics as opposed to linguist for a polyglot.

As for shepherd, its form in Old English is sceāphirde, so in a way it was shortened, but then lots of words were shortened in the transitions from Old to Middle to Present-Day English.

Ceci n'est pas un seing.