The Collaborative International Dictionary of English v.0.48:

Yesteryear \Yes"ter*year`\, n.
   The year last past; last year.
   [1913 Webster]

WordNet (r) 3.0 (2006):

yesteryear
    n 1: the time that has elapsed; "forget the past" [syn: past,
         past times, yesteryear] [ant: future, futurity,
         hereafter, time to come]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "yesteryear":
   bygone days, bygone times, days gone by, dead past, foretime,
   former times, history, lang syne, past, past history, past times,
   recent past, the irrevocable Past, the past, thou unrelenting past,
   times past, yesterday, yore