Etymology
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hexa- 
before vowels and in certain chemical compound words hex-, word-forming element meaning "six," from Greek hexa-, combining form of hex "six," from PIE root *sweks- (see six).
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-some (2)
suffix added to numerals meaning "a group of (that number)," as in twosome, from pronoun use of Old English sum "some" (see some). Originally a separate word used with the genitive plural (as in 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.
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