in·fre·quent /(ˌ)ɪnˈfrikwənt/
  (a.)稀少的,珍貴的,罕見的
  In·fre·quent a.  Seldom happening or occurring; rare; uncommon; unusual.
  The act whereof is at this day infrequent or out of use
  among all sorts of men.   --Sir T. Elyot.
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  infrequent
       adj : not frequent; not occurring regularly or at short intervals;
             "infrequent outbursts of temper" [ant: frequent]