trephination vs surgery

trephination and surgery both are nouns.

Word	Noun	Adjective	Verb	Adverb
trephination	Yes	No	No	No
surgery	Yes	No	No	No

As nouns, surgery is a hypernym of trephination; that is, surgery is a word with a broader meaning than trephination:

trephination: an operation that removes a circular section of bone from the skull
surgery: a medical procedure involving an incision with instruments; performed to repair damage or arrest disease in a living body

Other hypernyms of trephination include operation, surgical operation, surgical procedure, surgical process.

trephination (noun)	surgery (noun)
an operation that removes a circular section of bone from the skull	a medical procedure involving an incision with instruments; performed to repair damage or arrest disease in a living body
	a room in a hospital equipped for the performance of surgical operations
	a room where a doctor or dentist can be consulted
	the branch of medical science that treats disease or injury by operative procedures