Source : Webster's Revised Unabridged Dictionary (1913)

Aprosos \Ap"ro*sos`\, a. & adv. [F. ? propos; ? (L. ad) + propos
   purpose, L. proposium plan, purpose, fr. proponere to
   propose. See {Propound}.]
   1. Opportunely or opportune; seasonably or seasonable.

            A tale extremely apropos.             --Pope.

   2. By the way; to the purpose; suitably to the place or
      subject; -- a word used to introduce an incidental
      observation, suited to the occasion, though not strictly
      belonging to the narration.