get one's arse into gearto start to do something seriously and quickly
Also called (for senses 2, 3): arsehole (ˈɑːsˌhəʊl), (US and Canadian)asshole
Word Origin for arse
Dating back at least a thousand years, and taboo till around the middle of the 20th century, this venerable ``Anglo-Saxon'' word now seems unlikely to cause offence in all but the most formal contexts. Its acceptability has possibly been helped by such useful verb formations as ``to arse about'' and ``I can't be arsed''
"buttocks," Old English ærs "tail, rump," from Proto-Germanic *arsoz (cf. Old Saxon, Old High German, Old Norse ars, Middle Dutch ærs, German Arsch "buttock"), cognate with Greek orros "tail, rump, base of the spine," Hittite arrash, Armenian or "buttock," Old Irish err "tail." Middle English had arse-winning "money obtained by prostitution" (late 14c.).