Etymology
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oneiro- 

before vowels oneir-, word-forming element meaning "of or pertaining to a dream or dreams," from Greek oneiros "a dream," a word of uncertain origin, perhaps related to Armenian anurj, Albanian (Gheg) âdërrë.

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uni- 
word-forming element meaning "having one only," from Latin uni-, combining form of unus "one" (from PIE root *oi-no- "one, unique").
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hendeca- 
word-forming element meaning "eleven," from Latinized form of Greek hendeka "eleven," from hen, neuter of heis "one," from PIE *hems-, from root *sem- (1) "one; as one, together with" + deka "ten" (from PIE root *dekm- "ten").
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homeo- 

also homoeo-, word-forming element meaning "similar to," Latinized from Greek homio-, from homoios "like, resembling, of the same kind; equal," related to or an expanded form of homos "one and the same" (from PIE root *sem- (1) "one; as one, together with").

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homo- (1)

before vowels hom-, word-forming element meaning "same, the same, equal, like" (opposed to hetero-), from Greek homos "one and the same," also "belonging to two or more jointly" (from PIE *somo-, from root *sem- (1) "one; as one, together with").

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mono- 

word-forming element of Greek origin meaning "one, single, alone; containing one (atom, etc.)," from Greek monos "single, alone," from PIE root *men- (4) "small, isolated."

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hetero- 
before vowels heter-, word-forming element meaning "other, different," from Greek heteros "the other (of two), another, different; second; other than usual." It is a compound; the first element means "one, at one, together," from PIE root *sem- (1) "one; as one, together with;" the second is cognate with the second element in Latin al-ter, Gothic an-þar, Old English o-ðer "other."

Compounds in classical Greek show the range of the word there: Heterokretes "true Cretan," (that is, of the old stock); heteroglossos "of foreign language;" heterozelos "zealous for one side;" heterotropos "of a different sort or fashion," literally "turning the other way;" heterophron "raving," literally "of other mind."
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semper- 
word-forming element meaning "always, ever," from Latin semper "always, ever, at all times, continuously" (literally "once for all"), from PIE *semper-, from root *sem- (1) "one; as one, together with" + *per- "during, for."
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half- 
in genealogical combinations, "sharing one parent," Middle English, from half.
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xeno- 
before vowels, xen-, word-forming element meaning "strange, foreign; stranger, foreigner," from Greek xenos "a guest, stranger, foreigner, refugee, guest-friend, one entitled to hospitality," cognate with Latin hostis, from PIE root *ghos-ti- "stranger, guest, host." "The term was politely used of any one whose name was unknown" [Liddell & Scott].
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