(of similar things or occurrences) appearing or happening at irregular intervals in time; occasional

sporadic renewals of enthusiasm.

appearing in scattered or isolated instances, as a disease.

isolated, as a single instance of something; being or occurring apart from others.

occurring singly or widely apart in locality

the sporadic growth of plants.

adjective

constant , continuous , dependable

adjective

bits and pieces , desultory , few , fitful , fits and starts , hit-or-miss * , infrequent , intermittent , irregular , isolated , occasional , on-again-off-again , random , rare , scarce , scattered , seldom , semioccasional , spasmodic , spotty , uncommon , unfrequentnotes:periodic means happening or recurring at regular intervals; sporadic means occurring singly or occasionally or in scattered instances , periodic , periodical , unusual , separate , single