- fitting; at the right time; to the purpose; opportunely.
- Obsolete. by the way.
- opportune; pertinent: apropos remarks.
- apropos of, with reference to; in respect or regard to: apropos of the preceding statement.
- appropriate; pertinent
- appropriately or pertinently
- by the way; incidentally
- apropos of (preposition) with regard to; in respect of
1660s, “opportunely,” from French à propos “to the purpose,” from propos “thing said in conversation, talk; purpose, plan,” from Latin propositium “purpose,” past participle of proponere “to set forth, propose” (see propound). Meaning “as regards” is 1761, from French. As an adjective, “to the point or purpose,” from 1690s.
Concerning, in connection with, as in Apropos of keeping in touch, I haven’t heard from her in months. This idiom was a borrowing of the French à propos de (“to the purpose of”) in the 17th century. At first it was used without of and meant “fitting” or “opportune,” as in Their prompt arrival was very appropos. By the 1700s it was also being used with of, as in the current idiom, for “concerning” or “by way of.”