nonrecurring
isolated
one-off
go-round
one-shot
unoccasional
uncommonly
one-time
infrequent
rarely
unfrequent
unrecurrent
nonrecurrent
ever
recurrence
occasional
only when
only
nonrepetitional
nonsporadic
nonrepeated
only if
I can't remember the last time
episodic
expontaneous
stated
accidental
sporadical
nonincident
once-in-a-lifetime
seldom
rare
nonconsecutive
nonincidental
simultaneum
eternally
nonrare
once
yance
subchronic
casual
infrequently
rehash
periodically
sporadically
heterochronic
nonrecurrence
subfulminant
frequent
once in a while
at times
semioccasional
nonfrequent
from time to time
now and then
on occasion
occasionally
semioccasionally
hapax legomenon
acute
nonrepetition
now and again
once in a blue moon
semelincident
never
unique
lippening
non-occurring
incoincident
sporadic
common as pig tracks
transient
episodicity
right away
punctual
unrepetitive
recurring
harmonic
promptly
nonrepetitive
recurrent
unreminded
lightning never strikes twice in the same place
instantaneous
time of asking
unsuccessive
return
repeatlessness
instance
exceptional
concurrence
nongradual
recurringly
unrepeating