Source : Webster's Revised Unabridged Dictionary (1913)

Rearmouse \Rear"mouse`\, Reremouse \Rere"mouse`\, 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 \Rere"mouse`\ (r?r"mous`), n. (Zo["o]l.)
   A rearmouse.