perplexed

An interesting point. The OED notes that Latin had no verb *perplectere, only the adjective perplex-us, which looks like it's the past participle of such a verb, but might instead have come from per- "thoroughly" + the past participle plex-us of plect-ere "plait, interweave, entangle".

The English adjective was originally 'perplex', with the other words (verb and 'perplexed') derived from it.

After reading the conversation on rumoured, I just thought this one might interest you as well.
A similar reflection might be done about perplexed, I guess, at least in Italian.
Some (rather knowledgeable) people try to use the verb perplimere (something like to perplime) as the infinitive of perplexed.
The Accademia della Crusca states that it doesn't exist (it was made up for a comical TV show in the 90's), but as a back-formation it's very interesting indeed.
Is perplex a back-formation as well?