Source : Webster's Revised Unabridged Dictionary (1913)

Infrequently \In*fre"quent*ly\, adv.
   Not frequently; rarely.

Source : WordNet®

infrequently
     adv : not many times; "in your 1850 church you not infrequently
           find a dramatic contrast between the sumptuous
           appointments of the building itself and the inhuman
           barrack-like living conditions in the church room"
           [ant: {frequently}]