The Collaborative International Dictionary of English v.0.48:

Seep \Seep\, or Sipe \Sipe\, v. i. [AS. s[imac]pan to distill.]
   To run or soak through fine pores and interstices; to ooze.
   [Scot. & U. S.]
   [1913 Webster]

         Water seeps up through the sidewalks.    --G. W. Cable.
   [1913 Webster] Seepage

WordNet (r) 3.0 (2006):

seep
    v 1: pass gradually or leak through or as if through small
         openings [syn: seep, ooze]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "seep":
   bleed, condense, discharge, distill, dribble, drip, dripple, drop,
   effuse, emit, excrete, exfiltrate, extravasate, exudate, exude,
   filter, filtrate, flow, give off, gurgle, leach, leak, lixiviate,
   ooze, percolate, reek, sew, spurtle, strain, sweat, transpire,
   transude, trickle, weep