Source : Webster's Revised Unabridged Dictionary (1913)

Souvenir \Sou`ve*nir\ (? or ?), n. [F., fr. souvenir to
   remember, fr. L. subvenire to come up, come to mind; sub
   under + venire to come, akin to E. come. See {Come}, and cf.
   {Subvention}.]
   That which serves as a reminder; a remembrancer; a memento; a
   keepsake.

Source : WordNet®

souvenir
     n 1: something of sentimental value [syn: {keepsake}, {token}, {relic}]
     2: a reminder of past events [syn: {memento}]