The saying first appeared in the English language in 1668, borrowed from the French word “apropos,” meaning literally “to the purpose”. Since then, it has been used as an adverb, adjective, noun and preposition. It is a very versatile word. The correct pronunciation is ap-ra-po.
Sometimes it is used as a synonym for appropriate, but this is a deviation from its original meaning. Rarely it is used as a noun, when saying that which is referred to, has apropos – relevance ( noun) In French avoir de l’a propos.
” Apropos of Nothing”, the title of an autobiography by Woody Allen, is also an idiom, where the meaning is not deducible from the individual words. The action has no relevance to any previous discussion or situation – the opposite in fact to the usual meaning of apropos.
Used as a preposition, it leads on to further discussion of a subject of event, to which it refers. e.g ” apropos the proposed changes… ” As a preposition, apropos finds a place in formal letters. e.g ” apropos the receipt of the deed … ” Using it as an adjective, Charlotte Bronte wrote to her friend that ” Your letter coming is very apropos” If the wording of Charlotte’s letter had been ” Your letter arrived apropos” then Charlotte would have been using the word as an adverb.
If this is all Double Dutch to you, probably you will take the view that the word has indeed disappeared from general use. There is of course no reason not to use the word, either in spoken or written form, where it is relevant.
Bonne chance!