Why is the ninth month called September?
Old English sum "some, a, a certain one, something, a certain quantity; a certain number;" with numerals "out of" (e.g. sum feowra "one of four"); from Proto-Germanic *suma- (cf. Old Saxon, Old Frisian, Old High German sum, Old Norse sumr, Gothic sums), from PIE *smm-o-, suffixed form of root *sem- (1) "one," also "as one" (adv.), "together with" (see same). For substitution of -o- for -u-, see come.
The word has had greater currency in English than in the other Teutonic languages, in some of which it is now restricted to dialect use, or represented only by derivatives or compounds .... [OED]As a pronoun from c.1100; as an adverb from late 13c. Meaning "remarkable" is attested from 1808, American English colloquial. A possessive form is attested from 1560s, but always was rare. Many combination forms (somewhat, sometime, somewhere) were in Middle English but often written as two words till 17-19c. Somewhen is rare and since 19c. used almost exclusively in combination with the more common compounds; somewho "someone" is attested from late 14c. but did not endure. Scott (1816) has somegate "somewhere, in some way, somehow," and somekins "some kind of a" is recorded from c.1200. Get some "have sexual intercourse" is attested 1899 in a quote attributed to Abe Lincoln from c.1840.
word-forming element used in making adjectives from nouns or adjectives (and sometimes verbs) and meaning "tending to; causing; to a considerable degree," from Old English -sum, identical with som (see some). Cf. Old Frisian -sum, German -sam, Old Norse -samr; also related to same.
suffix added to numerals meaning "a group of (that number)," e.g. twosome, from pronoun use of Old English sum "some" (see some). Originally a separate word used with the genitive plural (e.g. sixa sum "six-some"); the inflection disappeared in Middle English and the pronoun was absorbed. Use of some with a number meaning "approximately" also was in Old English.
word-forming element meaning "the body," Modern Latin, from Greek soma "the body" (see somato-).
Very good; very effective; real • Often used ironically: In three weeks England will have her neck wrung like a chicken. Some neck! Some chicken! (1808+)