head ache vs cephalalgia

head ache and cephalalgia both are nouns.

Word	Noun	Adjective	Verb	Adverb
head ache	Yes	No	No	No
cephalalgia	Yes	No	No	No

As nouns, head ache and cephalalgia are synonyms defined as:

head ache and cephalalgia: pain in the head caused by dilation of cerebral arteries or muscle contractions or a reaction to drugs

Other synonyms of head ache include headache.

head ache (noun)	cephalalgia (noun)
pain in the head caused by dilation of cerebral arteries or muscle contractions or a reaction to drugs	pain in the head caused by dilation of cerebral arteries or muscle contractions or a reaction to drugs