From WordNet (r) 2.0 (August 2003) [wn]:
occasionally
adv : 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: 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]