Definition of Allen wrench in US English:

Allen wrench

(also allen wrench)

noun

US
trademark
  • An L-shaped metal bar with a hexagonal head at each end, used to turn bolts and screws having hexagonal sockets.

    British term Allen key

Origin

Early 20th century: from the name of the manufacturer, the Allen Manufacturing Company, of Hartford, Connecticut.

Pronunciation

Allen wrench

/ˈalən ˌrenCH/