1) Far apart in space 2) Few and far between 3) Intermittent 4) Irregular 5) Not frequent 6) Occasional 7) Rare 8) Special 9) Sporadic 1) Few 2) Irregular 3) Occasional 4) Rare 5) Scarce 6) Seldom 7) Sporadic 8) Unusual 
• (a.) Seldom happening or occurring; rare; uncommon; unusual.
In·fre'quent adjective [ Latin infrequens : confer French infrequent . See In- not, and Frequent .] 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. Ely...
[adj] - not frequent
adjective not frequent; not occurring regularly or at short intervals; `infrequent outbursts of temper`
happening or occurring at long intervals or rarely: infrequent visits. · not constant, habitual, or regular: an infrequent visitor. · not plentiful or many: infrequent opportunities for advancement. · far apart in space.
not occurring regularly or at short intervals