PalLaws1(1) 28:34 :עד יתיילד לה מום‏ : until a blemish appears on it
See the entire entry for yld vb. to give birth; C to produce

PalLaws1(1) 28:34 :עד יתיילד לה מום‏ : until a defect develops in it
See the entire entry for mūm, mūmā n.m. defect

PalLaws1(1) 28:34 :אסיר לך למכוס יתה עד יתיילד לה מום וישתרי למכו‏ : it is forbidden to slaughter it (i.e. the firstborn animal) until a blemish appears, and then it is permitted to slaughter
See the entire entry for šry vb. to loosen; D to begin