episodic
occasionally
on occasion
at times
once in a while
now and again
from time to time
now and then
episodicity
semiperiodic
occasional
on-again, off-again
quasiperiodic
periodical
periodic
every so often
sporadically
erratically
on an irregular basis
punctual
infrequent
recurrence
unfrequent
heterochronic
on a regular basis
unregular
recurringly
on and off
seldom
sporadic
return
periodically
stated
eternally
accidental
choppy
habitually
here and there
adventitiously
harmonic
roll around
intermittently
stop-start
come around
uncommonly
I can't remember the last time
seldomness
pulsation
casual
recurring