now and then is an adverb meaning "sporadically and infrequently". It carries one recorded sense.
sporadically and infrequently
“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”
Definitions, synonyms and semantic relations for now and then come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.