“blow” – English explanatory dictionary

noun 1. a knock or punch ○ He received a blow to the head in the fight. 2. a shock, which comes from bad news ○ The election result was a blow to the government. ■ verb 1. to make air move ○ The wind had been blowing hard all day. ○ Blow on your soup if it’s too hot. □ to blow your nose to clear a blocked nose by blowing down it into a handkerchief ○ She has a cold and keeps having to blow her nose. 2. □ to blow a fuse to burn out a fuse by making too much electricity flow through it

to expose, or inform; “BLOW the gaff,” to inform against a
person.

“‘As for that,’ says Will, ‘I could tell it well enough, if I had
it, but I must not be seen anywhere among my old acquaintances, for
I am BLOWN, and they will all betray me.’”—_History of Colonel
Jack_, 1723.

The expression would seem to have arisen from the belief that a flower
might be blighted if “BLOWN upon” by a foul wind or a corrupted breath.
See the condition of the flowers on a dinner-table by the time the
company rise. In _America_, “to BLOW” is slang for to lie in a boasting
manner, to brag or “gas” unduly.

(blo), v. i. [imp. Blew (blu); p. p. Blown (blon); p. pr. & vb. n. Blowing.] [OE. blowen, AS. blowan to blossom; akin to OS. blojan, D. bloeijen, OHG. pluojan, MHG. blüejen, G. blühen, L. florere to flourish, OIr. blath blossom. Cf. Blow to puff, Flourish.] To flower; to blossom; to bloom. “How blows the citron grove.
Milton.”

v. t. To cause to blossom; to put forth (blossoms or flowers). “The odorous banks, that blow
Flowers of more mingled hue.
Milton.”

n. (Bot.) A blossom; a flower; also a state of blossoming; a mass of blossoms. ´Such a blow of tulips.´ Tatler.