lesser ape vs siamang

lesser ape and siamang both are nouns.

Word	Noun	Adjective	Verb	Adverb
lesser ape	Yes	No	No	No
siamang	Yes	No	No	No

As nouns, siamang is a hyponym of lesser ape; that is, siamang is a word with a more specific, narrower meaning than lesser ape:

lesser ape: gibbons and siamangs
siamang: large black gibbon of Sumatra having the 2nd and 3rd toes partially united by a web

Other hyponyms of lesser ape include gibbon, Hylobates lar, Hylobates syndactylus, Symphalangus syndactylus.

lesser ape (noun)	siamang (noun)
gibbons and siamangs	large black gibbon of Sumatra having the 2nd and 3rd toes partially united by a web