Noun
Diminutive for Mouse.
Source: Webster's dictionaryGeorge insults and mocks Honey with an extemporaneous tale of "the Mousie" who "tooted brandy immodestly and spent half her time in the upchuck". Source: Internet
On Monday morning, DeChantal got about 30 live viewers for her first video, in which she read “Mousie, I Will Read to You” and “The Night Library.” Source: Internet
But as with many nicknames, “Mousie” stuck. Source: Internet