The Collaborative International Dictionary of English v.0.48:

Pester \Pes"ter\ (p[e^]s"t[~e]r), v. t. [imp. & p. p.
   Pestered; p. pr. & vb. n. Pestering.] [Abbrev. fr.
   impester, fr. OF. empaistrier, empestrer, to entangle the
   feet or legs, to embarrass, F. emp[^e]trer; pref. em-, en-
   (L. in in) + LL. pastorium, pastoria, a fetter by which
   horses are prevented from wandering in the pastures, fr. L.
   pastorius belonging to a herdsman or shepherd, pastor a
   herdsman. See In, and Pasture, Pastor.]
   1. To trouble; to disturb; to annoy; to harass with petty
      vexations.
      [1913 Webster]

            We are pestered with mice and rats.   --Dr. H. More.
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            A multitude of scribblers daily pester the world.
                                                  --Dryden.
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   2. To crowd together in an annoying way; to overcrowd; to
      infest. [Obs.] --Milton.
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            All rivers and pools . . . pestered full with
            fishes.                               --Holland.
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WordNet (r) 3.0 (2006):

pester
    v 1: annoy persistently; "The children teased the boy because of
         his stammer" [syn: tease, badger, pester, bug,
         beleaguer]