Origin of titmouse
- Alteration (influenced by mous mouse) of Middle English titmose tit- (probably from Old Norse tittr small peak, pin, titmouse) mose titmouse (from Old English māse)
From American Heritage Dictionary of the English Language, 5th Edition
- From Middle English titmose, compound of tit (“small bird") and Old English mÄse (“titmouse"), from Proto-Germanic *maisÇ (compare Dutch mees, German Meise, Old Norse meisingr), from *maisaz (“tiny, puny") (compare Norwegian meis (“skinny weakling")). The plural is formed in imitation of the otherwise unrelated mouse.