adverb (r)

• not many times(adv.all)

  Example:
  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.
  

  Antonym:
  frequently, oft, often, oftentimes, ofttimes
  

  source: wordnet30
• Not frequently; rarely.(adverb)

  source: webster1913