tit vs blue tit

tit and blue tit both are nouns.

Word	Noun	Adjective	Verb	Adverb
tit	Yes	No	No	No
blue tit	Yes	No	No	No

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

tit: small insectivorous birds
blue tit: widely distributed European titmouse with bright cobalt blue wings and tail and crown of the head

tit (noun)	blue tit (noun)
small insectivorous birds	widely distributed European titmouse with bright cobalt blue wings and tail and crown of the head
either of two soft fleshy milk-secreting glandular organs on the chest of a woman
the small projection of a mammary gland