noun, verb, -sured, -sur⋅ing.| 1. | a narrow opening produced by cleavage or separation of parts. |
| 2. | cleavage (def. 1). |
| 3. | Anatomy. a natural division or groove in an organ, as in the brain. |
| 4. | to make fissures in; cleave; split. |
| 5. | to open in fissures; become split. |
fissure fis·sure (fĭsh'ər)
n.
A deep furrow, cleft, or slit.
A developmental break or fault in the enamel of a tooth.