A titmouse is a very small insectivorous bird that come from the family Paridae and are only found in the northen hemisphere and Africa.
The name titmouse is attested from the 14th century, composed of the Old English name for the bird, mase (Proto-Germanic *maison) and tit, denoting something small. The spelling was influenced by mouse in the 16th century.
A phrase used to denote a woman who is, mostly, tits. This term is mostly reserved for use with tits that hang excessively and in most cases swing while in motion.