a narrow opening produced by cleavage or separation of parts.

cleavage ( def. 1 ) .

Anatomy . a natural division or groove in an organ, as in the brain.

to make fissures in; cleave; split.

to open in fissures; become split.

noun

cleft , cleavage , crack , crevice , hole , break , chink , rift , split , alienation , disaffection , estrangement , rent , rupture , schism , aperture , blemish , breach , chasm , cranny , crevasse , division , flaw , furrow , gap , groove , leak , lesion , opening , rima , rime , seam , slit , sulcus , vein

verb

fracture , rupture , split