cleft (n.)

synonym: fissure
https://doi.org/10.1351/goldbook.10531
Gap in soft tissue, bone, or both.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 737 (https://doi.org/10.1515/pac-2015-1202)