at arm's length

: a human upper limb

: something like or corresponding to an arm: such as

: the forelimb of a vertebrate

: to furnish or equip with weapons

: to furnish with something that strengthens or protects

: to equip or ready for action or operation

: a means (such as a weapon) of offense or defense

: a combat branch (as of an army)

: an organized branch of national defense (such as the navy)

: the longer or longest dimension of an object

: a measured distance or dimension — see Metric System Table, Weights and Measures Table

: the quality or state of being long