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