From WordNet (r) 3.0 (2006) [wn]:
occasionally
adv 1: now and then or here and there; "he was arrogant and
occasionally callous"; "open areas are only occasionally
interrupted by clumps of trees"; "they visit New York on
occasion"; "now and again she would take her favorite
book from the shelf and read to us"; "as we drove along,
the beautiful scenery now and then attracted his
attention" [syn: occasionally, on occasion, {once in
a while}, now and then, now and again, at times,
from time to time]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Occasionally \Oc*ca"sion*al*ly\, adv.
In an occasional manner; on occasion; at times, as
convenience requires or opportunity offers; not regularly.
--Stewart.
[1913 Webster]
The one, Wolsey, directly his subject by birth; the
other, his subject occasionally by his preferment.
--Fuller.
[1913 Webster]