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uni- (Prefix) "one"
From Latin uni- 'id.' From unus "one" (see uno).
único (Adjective) "only," "unique"
Late 15th cent. From Latin unicus 'id.' From unus "one" (see uno) and -icus, diminutive sufix (see -ico).
Indo-European
Romance
Portuguese único, Catalan únic, French unique
unidad f. (Noun) "unity"
13th cent. From Latin unitatem, accusative of unitas 'id.' Derived from unus "one" (see uno).
Indo-European
Romance
French unité, Italian unità
unir (Verb) "to join"
16th cent. From Late Latin unire 'id.,' a verb formed from Latin unus "one" (see uno).
universidad f. (Noun) "university"
Borrowed from Medieval Latin universitatem, accusative of universitas "university," but originally meaning "all things." From universus "all turned to one" (see universo).
Indo-European
Romance
Asturian universidá, Portuguese universidade, Catalan universitat, French université, Italian università
universo m. (Noun) "universe"
Borrowed from Latin universum "all things turned in one;" "universe." From uni- "one" (see uni-) and versus "turn" (see verso).
Indo-European
Romance
Portuguese universo, Catalan univers, French univers, Italian universo, Romanian univers
uno (Cardinal Number) "one"
10th cent. From Latin unus 'id.' Old Latin oino, accusative singular masculine of *oinos. From Proto-Italic *oino- 'id.' From late Proto-Indo-European *Hoi̯-no- 'id.' The first element *Hoi̯- is possibly from Proto-Indo-European *h1ei̯- "this/that."
Indo-European
Romance
Asturian unu, Portuguese um, Galician un, Catalan un, French un, Italian uno, Aromanian un, Romanian unu, Sardinian unu
Italic
Oscan uns "one," Umbrian uinus 'id.'
Celtic
Old Irish óen "one," Middle Welsh un 'id.,' Old Breton un 'id.,' Cornish un 'id.'
Germanic
Gothic ains "one," Old Norse einn "id.," Old High German ein 'id.,' Old Saxon ēn 'id.,' Old English ān 'id.' (English one)
Albanian
Albanian një "one"
Balto-Slavic
Serbian Chuch Slavic inъ "someone," Russian inój "other," Czech jiný 'id.,' Polish inny 'id.,' Slovene in 'id.,' Old Prussian ainan "one," Lithuanian víenas 'id.,' Latvian viêns 'id.'
Hellenic
Ancient Greek οἴνη (oíne) "one (on dice)"
Indo-Iranian
Sanskrit éka- "one," Avestan aēuua- 'id.'
-ura Suffix forming abstract nouns from adjectives.
From Latin -ura 'id.' From the -u- in the past participle (e.g., pass-ere > pass-u-s) and suffix -ra, a descriptive noun-forming suffix from adjectives. Of unknown origin.

It is possible the suffix is somehow from the feminine Proto-Italic adjective suffix *-rā (masc. *-ro-), in which case it reflects Core Proto-Indo-European *-r-eh2, a feminine derivative of Proto-Indo-European *-ro-. Adding to the evidence are -t/s- extensions in Latin (-tura, sura), a common process with native suffices. Unfortunately, the theory does not answer the question of how a feminine adjective-forming suffix came to form abstract feminine nouns from adjectives.

Another tempting solution is that the suffix is a borrowing, or the result of semantic influence, from the Etruscan suffix -ra, which formed adjectives and nouns.
Indo-European
Romance
Asturian -ura, Portuguese -ura, Galician -ura, Italian -ura
usanza f. (Noun) "usage;" "custom"
Late 15th cent. From usar and -anza, a noun-forming suffix added to verbs indicating a condition.
usar (Verb) "to use"
Very early 13th cent. From Vulgar Latin *usare 'id.,' from Latin uti "to use" (Old Latin œti) and frequentive suffix -are (see note under faltar). From Proto-Italic *oit-e/o- 'id.' Probably from Proto-Indo-European *h3ei̯t- "to fetch," "to take along."
Indo-European
Italic
Paelignian oisa "used"
Hellenic
Ancient Greek οἴσω (oíso) "I bring"