Adverbs of Time and Place - Adverbs of Low Frequency

not at any point in time

on any occasion

in a manner that almost does not occur or happen

for one single time

for a single instance

for two instances

on a very infrequent basis

used to refer to something that happens rarely or infrequently

on very rare occasions

in an infrequent and unpredictable manner

not on regular occasions

not on a regular basis

on irregular but not rare occasions

on occasions that are not regular or frequent

at moments that are not constant or regular

at infrequent intervals

at irregular intervals