Why is the ninth month called September?
"move air," Old English blawan "blow, breathe, make an air current; kindle; inflate; sound a wind instrument" (class VII strong verb; past tense bleow, past participle blawen), from Proto-Germanic *blæ-anan (cf. Old High German blaen, German blähen), from PIE *bhle- "to swell, blow up" (cf. Latin flare "to blow"), possibly identical with *bhel- (2) "to blow, swell" (see bole).
Meaning "to squander" (of money) is from 1874. Sense of "depart suddenly" is from 1902. Slang "do fellatio on" sense is from 1933, as blow (someone) off, originally among prostitutes (cf. blow job). This usage probably is not connected to the colloquial imprecation (1781, associated with sailors, e.g. Popeye's "well, blow me down!"), which has past participle blowed. Meaning "to spend (money) foolishly and all at once" is 1890s; that of "bungle an opportunity" is from 1943. To blow over "pass" is from 1610s, originally of storms. To blow (someone's) mind was in use by 1967; there is a song title "Blow Your Mind" released in a 1965 Mirawood recording by a group called The Gas Company.
"to bloom, blossom" (intransitive), from Old English blowan "to flower, blossom, flourish," from Proto-Germanic *blæ- (cf. Old Saxon bloian, Old Frisian bloia, Middle Dutch and Dutch bloeien, Old High German bluoen, German blühen), from PIE *bhle-, extended form of *bhel- (2) "to blow, inflate, swell" (see bole). This word is the source of the blown in full-blown.
"hard hit," mid-15c., blowe, from northern and East Midlands dialects, perhaps from Middle Dutch blouwen "to beat," a common Germanic word of unknown origin (cf. German bleuen, Gothic bliggwan "to strike"). Influenced in English by blow (v.1). In reference to descriptions or accounts, blow-by-blow is recorded from 1921, American English, originally of prize-fight broadcasts.
LIKE a hungry kitten loves its saucer of warm milk, so do radio fans joyfully listen to the blow-by-blow broadcast description of a boxing bout. ["The Wireless Age," December 1922]
"a blowing, a blast," 1650s, from blow (v.1).
blow someone away, blow one's cool, blow someone's or something's cover, blow someone's mind, blow off one's mouth, blow the gaff, blow the lid off, blow the whistle, blow up, blow up a storm, blow something wide open, let off steam, low blow, one-two