1. an arm and a leg, a great deal of money: to cost an arm and a leg. 2. arm in arm, with arms linked together or intertwined: They walked along arm in arm. 3. at arm's length, on terms lacking in intimacy; at a distance: to keep business associates at arm's length. 4. in the arms of Morpheus, asleep.5. put the arm on, Slang. a. to solicit or borrow money from.. arm in arm, with arms linked together or intertwined: They walked along arm in arm. 3. at arm's length, on terms lacking in intimacy; at a distance: to keep business associates at arm's length. 4. in the arms of Morpheus, asleep. 5. put the arm on, Slang.