WordNet (r) 3.0 (2006):

annum
    n 1: (Latin) year; "per annum"

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "annum":
   abundant year, academic year, bissextile year, calendar month,
   calendar year, century, common year, day, decade, decennary,
   decennium, defective year, fiscal year, fortnight, hour, leap year,
   lunar month, lunar year, lunation, luster, lustrum, man-hour,
   microsecond, millennium, millisecond, minute, moment, month, moon,
   quarter, quinquennium, regular year, second, semester, session,
   sidereal year, solar year, sun, term, trimester, twelvemonth, week,
   weekday, year