E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
To draw the longbow. To exaggerate. The force of an arrow in the longbow depends on the strength of the arm that draws it, so the force of a statement depends on the force of the speakers imagination. The longbow was the favourite weapon of the English from the reign of Edward II. till it was superseded by fire-arms. The longbow was the hand-bow, as distinguished from the crossbow or bow fitted on a stock.