tiger vs Bengal tiger

tiger and Bengal tiger both are nouns.

Word	Noun	Adjective	Verb	Adverb
tiger	Yes	No	No	No
Bengal tiger	Yes	No	No	No

As nouns, Bengal tiger is a hyponym of tiger; that is, Bengal tiger is a word with a more specific, narrower meaning than tiger:

tiger: large feline of forests in most of Asia having a tawny coat with black stripes; endangered
Bengal tiger: southern short-haired tiger

Other hyponyms of tiger include tiger cub, tigress.

tiger (noun)	Bengal tiger (noun)
large feline of forests in most of Asia having a tawny coat with black stripes; endangered	southern short-haired tiger
a fierce or audacious person