tomtit vs titmouse

tomtit and titmouse both are nouns.

Word	Noun	Adjective	Verb	Adverb
tomtit	Yes	No	No	No
titmouse	Yes	No	No	No

As nouns, titmouse is a hypernym of tomtit; that is, titmouse is a word with a broader meaning than tomtit:

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

Other hypernyms of tomtit include tit.

tomtit (noun)	titmouse (noun)
widely distributed European titmouse with bright cobalt blue wings and tail and crown of the head	small insectivorous birds