Medical Definition of effacement
: the thinning or obliteration of tissue or narrowing of an internal anatomical space <effacement of the spinal subarachnoid space>; especially : the shortening and thinning of the uterine cervix during labor so that only the external orifice remains <Though far from strong enough to bring your baby into the world, late-third-trimester Braxton Hicks contractions contribute to the effacement and dilation of the cervix …—Arlene Eisenberg et al., Parenting, June/July 1996>
efface\-ˈfās\play transitive verb
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