Antonyms for infrequent
ɪnˈfri kwənt

infrequent(adj)
not frequent; not occurring regularly or at short intervals
"infrequent outbursts of temper"
Antonyms:
frequent, prevalent, steady, prevailing, dominant, rife, regular, predominant

infrequent
Unique is alone of its kind; rare is infrequent of its kind; great poems are rare; "Paradise Lost" is unique. To say of a thing that it is rare is simply to affirm that it is now seldom found, whether previously common or not; as, a rare old book; a rare word; to call a thing scarce implies that it was at some time more plenty, as when we say food or money is scarce. A particular fruit or coin may be rare; scarce applies to demand and use, and almost always to concrete things; to speak of virtue, genius, or heroism as scarce would be somewhat ludicrous. Rare has the added sense of precious, which is sometimes, but not necessarily, blended with that above given; as, a rare gem. Extraordinary, signifying greatly beyond the ordinary, is a neutral word, capable of a high and good sense or of an invidious, opprobrious, or contemptuous signification; as, extraordinary genius; extraordinary wickedness; an extraordinary assumption of power; extraordinary antics; an extraordinary statement is incredible without overwhelming proof.
See synonyms for GENERAL; NORMAL; USUAL.
Synonyms:
curious, extraordinary, incomparable, odd, peculiar, precious, rare, remarkable, scarce, singular, strange, uncommon, unique, unparalleled, unprecedented, unusual

Adrian Baker:
We just thought that was the result of my dad being away from her for the last five days, which was very very very infrequent in their lives together.
Claire Simeone:
Certainly it is concerning because it’s happened twice in 24 hours, we know that historically these bites are pretty infrequent.
Eric Day:
Communities and farms with large numbers of cicadas emerging at once may have a substantial noise issue, hopefully, any annoyance at the disturbance is tempered by just how infrequent -- and amazing -- this event is.
Rita Colwell:
These are interesting organisms and range in scale from massive global epidemics -- cholera -- to infrequent but lethal infections -- Vibrio vulnificus.
Martin Cetron:
The problem is most of the time when International IHRs do contact investigations the time window for measles is narrow... International IHRs are hearing about it after the fact so [ International IHRs ] ability to know about cases before they travel is infrequent.