Vaux Vocab. of the Flash Lang. in McLachlan (1964) 225: arm-pits: To work under the arm-pits, is to practise only such kinds of depredation, as will amount, upon conviction, to what the law terms single, or petty larceny; the extent of punishment for which is transportation for seven years. By following this system, a thief avoids the halter, which certainly is applied above the arm-pits.at work under the armpits (v.) under armpit, n.