pectoral muscle vs pecs

pectoral muscle and pecs both are nouns.

Word	Noun	Adjective	Verb	Adverb
pectoral muscle	Yes	No	No	No
pecs	Yes	No	No	No

As nouns, pectoral muscle and pecs are synonyms defined as:

Other synonyms of pectoral muscle include musculus pectoralis, pectoral, pectoralis.

pectoral muscle (noun)	pecs (noun)
either of two large muscles of the chest	either of two large muscles of the chest