Himalayas vs Himalaya

Himalayas and Himalaya both are nouns.

Word	Noun	Adjective	Verb	Adverb
Himalayas	Yes	No	No	No
Himalaya	Yes	No	No	No

As nouns, Himalayas and Himalaya are synonyms defined as:

Himalayas and Himalaya: a mountain range extending 1500 miles on the border between India and Tibet; this range contains the world's highest mountain

Other synonyms of Himalayas include Himalaya Mountains.

Himalayas (noun)	Himalaya (noun)
a mountain range extending 1500 miles on the border between India and Tibet; this range contains the world's highest mountain	a mountain range extending 1500 miles on the border between India and Tibet; this range contains the world's highest mountain