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]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "souvenir":
   Mnemosyne, affect memory, anterograde memory, atavism,
   collective memory, commemoration, computer memory, disk memory,
   drum memory, emotional response, engram, favor,
   information storage, keepsake, kinesthetic memory, memento,
   memento mori, memorabilia, memorial, memorials, memories, memory,
   memory bank, memory circuit, memory trace, mind, mneme,
   race memory, recollection, relic, remembrance, remembrancer,
   reminder, screen memory, skill, tape memory, token,
   token of remembrance, trophy, verbal response, visual memory