The Collaborative International Dictionary of English v.0.48:

lower limit \lower limit\, lower-limit \lower-limit\n.
   the limit on the lower (or southernmost) side of something.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

lower limit
    n 1: the smallest possible quantity [syn: minimum, lower
         limit] [ant: maximum, upper limit]
    2: the limit on the lower (or southernmost) side of something