The Collaborative International Dictionary
Reremouse
Rearmouse \Rear"mouse`\, Reremouse \Rere"mouse`\ (-mous`), n. [AS. hr[=e]rem[=u]s; probably fr. hr[=e]ran to agitate, stir (akin to G. r["u]hren, Icel. hr[ae]ra) + m[=u]s mouse.] (Zo["o]l.) The leather-winged bat ( Vespertilio murinus). [Written also reermouse.]
Reremouse
Reremouse \Rere"mouse`\ (r?r"mous`), n. (Zo["o]l.) A rearmouse.
Wiktionary
reremouse
n. (context heraldry English) A bat (gloss: flying mammal)