occasionally

adverb

1. Once in a while; at times: betimes, intermittently, periodically, sometimes, sporadically. Idioms: ever andagainanon, now andagainthen. See continue/stop/pause.
2. At rare intervals: infrequently, little, rarely, seldom, sporadically. Idioms: hardlyscarcelyever, once in a blue moon. See usual/unusual.

Definition: every now and then
Antonyms: always, constantly, frequently, often, regularly, steadily, usually

The adverb has one meaning:

Meaning #1: now and then or here and there
  Synonyms: on occasion, once in a while, now and then, now and again, at times, from time to time
  Derived from adjective: occasional (meaning #1)