cervix vs bull neck

cervix and bull neck both are nouns.

Word	Noun	Adjective	Verb	Adverb
cervix	Yes	No	No	No
bull neck	Yes	No	No	No

As nouns, bull neck is a hyponym of cervix; that is, bull neck is a word with a more specific, narrower meaning than cervix:

cervix: the part of an organism (human or animal) that connects the head to the rest of the body
bull neck: a thick short powerful neck

cervix (noun)	bull neck (noun)
the part of an organism (human or animal) that connects the head to the rest of the body	a thick short powerful neck
necklike opening to the uterus