The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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