Old English handle, formed from hand (n.) with instrumental suffix -le indicating a tool in the way thimble was formed from thumb. The slang sense of "nickname" is first recorded 1870, originally U.S., from earlier expressions about adding a handle to (one's) name, i.e. a title such as Mister or Sir, attested from 1833. To fly off the handle (1833) is a figurative reference to an ax head (to be off the handle "be excited" is recorded from 1825, American English). To get a handle on "get control of" is first recorded 1972.
Old English handlian "to touch or move with the hands," also "deal with, discuss;" see handle (n.). Akin to Old Norse höndla "to seize, capture," Danish handle "to trade, deal," German handeln "to bargain, trade." Related: Handled; handling. Meaning "to act towards (someone) in a certain manner" (usually with hostility or roughness) is from c.1200. The commercial sense was weaker in English than in some other Germanic languages, but it emerged in American English (1888) from the notion of something passing through one's hands, and cf. handler.
To cope with; manage; hack: He can handle Tom's temper tantrums very well/ My wife left me and I don't know how to handle it (1970s+)