(To). As the wind blows; or to blow with the breath. (Anglo-Saxon, blawan, to blow or breathe.) It will soon blow over. It will soon be no longer talked about; it will soon come to an end, as a gale or storm blows over or ceases.
To blow off is another form of the same phrase.
To blow great guns. The wind blows so violently that its noise resembles the roar of artillery. To blow hot and cold, (or) To blow hot and cold with the same breath. To be inconsistent. The allusion is to the fable of a traveller who was entertained by a satyr. Being cold, the traveller blew his fingers to warm them, and afterwards blew his hot broth to cool it. The satyr, in great indignation, turned him out of doors, because he blew both hot and cold with the same breath.
To blow off the steam. To get rid of superfluous energy. The allusion is to the forcible escape of superfluous steam no longer required.
2. Blow (To). To sound a trumpet.
But when the blast of war blows in our ears, Let us be tigers in our fierce deportment.
Shakespeare: Henry V., iii. 1.
To blow. To inform against a companion; to “peach.” The reference is to the announcing of knights by blast of trumpet.
3. Blow (To). To blast as with gunpowder.
I will blow him up sky high. Give him a good scolding. A regular blowing up is a thorough jobation. The metaphor is from blasting by gunpowder.
But to blow up a bladder, etc., means to inflate it.
4. Blow. A stroke. (German, bläuen, to beat or strike.)
At one blow. By one stroke.
The first blow is half the battle. Well begun is half done. Pythagoras used it. say, “The beginning is half the whole.” “Incipe: Dimidium facti est coepisse” (Ausonius). “Dimidium facti, qui coepit, habet” (Horace). “Ce n'est que le premier pas qui coûte.”
Without striking a blow. Without coming to a contest.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894