keep at arm's length, to

To avoid familiarity, to keep someone at a distance. This expression, with its inevitable image of extending one’s arm to push someone away, has long been used figuratively to signify distancing oneself from a problem, group, political stand, and so forth. In the sixteenth century it was put as at arm’s end, as Sir Philip Sidney had it in Arcadia (1580), but by the mid-seventeenth century it began to appear as at arm’s length.