Medical Definition of bulb
1: a rounded dilation or expansion of something cylindrical <the bulb of a thermometer>; especially : a rounded or pear-shaped enlargement on a small base <the bulb of an eyedropper>
2: a rounded part: asa: a rounded enlargement of one end of a part—see bulb of the penis, bulb of the vestibule, end bulb, hair bulb, olfactory bulbb: medulla oblongata; broadly : the hindbrain exclusive of the cerebellumc: a thick-walled muscular enlargement of the pharynx of certain nematode worms
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