Etymology Dictionary

BAT (1),  a short cudgel.  (C.)   M.E. batte, Prompt. Parv. p. 26; botte, Ancren Riwle, p. 366; Layamon, 21593.—Irish and Gaelic bat, bata, a staff, cudgel; cf. Bret. bataraz, a club.   Perhaps this furnishes the root of Lat. batuere; see note to Beat.   Der. bat-let (with dimin. suffix -let = -el-et), a small bat for beating washed clothes; Shak., As You Like It, ii. 4. 49.   Also bat, verb; Prompt. Parv.   ¶ Lye gives an A.S. bat, but without a reference; and it was probably merely borrowed from O. British.   Cf. pat.

BAT (2),  a winged mammal.  (Scand.)   Corrupted from M.E. bakke.   The Prompt. Parv. has 'Bakke, flyinge best [beast], vespertilio.'   Wyclif has backe, Levit. xi. 19.—Dan. bakke, only used in the comp. aftenbakke, evening-bat.   For change of k to t, cf. mate from M.E. make.   β. Bakke stands for an older blakke, seen in Icel. leðr-blaka = a 'leather-flapper,' a bat.—Icel. blaka, to flutter, flap.   ¶ The A.S. word is hréremús, whence prov. Eng. reremouse, rearmouse.