'Shrug' definitions:

Definition of 'shrug'

noun

A gesture involving the shoulders

verb

Raise one's shoulders to indicate indifference or resignation

From: GCIDE

Shrug \Shrug\ (shr[u^]g), v. t. [imp. & p. p. Shrugged (shr[u^]gd); p. pr. & vb. n. Shrugging (shr[u^]g"g[i^]ng).] [Probably akin to shrink, p. p. shrunk; cf. Dan. skrugge, skrukke, to stoop, dial. Sw. skrukka, skruga, to crouch.] To draw up or contract (the shoulders), especially by way of expressing doubt, indifference, dislike, dread, or the like. [1913 Webster]
He shrugs his shoulders when you talk of securities. --Addison. [1913 Webster]

From: GCIDE

Shrug \Shrug\, v. i. To raise or draw up the shoulders, as in expressing doubt, indifference, dislike, dread, or the like. [1913 Webster]
They grin, they shrug. They bow, they snarl, they snatch, they hug. --Swift. [1913 Webster]

From: GCIDE

shrug \shrug\, n. A gesture consisting of drawing up the shoulders, -- a motion usually expressing doubt, indifference, or dislike; -- it is sometimes accompanied by a slight turning of the hands outward or upward. Such a gesture may be made, as in answering "who knows" to a question, suggesting utter ignorance of an answer and a disinclination to pursue the topic further. [1913 Webster +PJC]
On Sept. 23, in a major speech in New York, the chairman of the Securities and Exchange Commision, Arthur Levitt asked the Big Board to spike the rule [Rule 390] in the interest of free and unfettered markets. . . . Mr. Grasso responded with a shrug, saying that he had no plans to kill the rule. --Gretchen Morgenson (N. Y. Times Nov.
28, 1999 sect. 3 p. 1. [PJC]
The Spaniards talk in dialogues Of heads and shoulders, nods and shrugs. --Hudibras. [1913 Webster]