shrug v.

late 14c., shruggen, "raise or draw up (the shoulders) with a sudden movement," a word of uncertain origin, perhaps connected to Danish skrugge "to stoop, crouch." From c. 1600 generally as an expression of doubt, indifference, etc., but it isn't clearly so in the earliest uses. It also could mean "to shrink, to shiver," as with cold (mid-15c.). Related: Shrugged; shrugging. Figurative use of shrug (something) off "be indifferent to" is by 1909.

"shoulder motion meant to express indifference, doubt, want of an answer, etc.," 1590s, from shrug (v.). The earliest references often are to stage acting, and treat the gesture as somehow foreign; it is described variously a Neapolitan, Spanish, or French shrug in OED's early citations.