The only free and comprehensive online etymological dictionary of the Spanish language
oscuridad f. (Noun) "darkness"
13th cent. From Latin oscuritatem, accusative of obscuritas 'id.' Derived from obscurus "dark" (see oscuro).
Indo-European
Romance
Asturian escuridá, Portuguese obscuridade, French obscurité, Italian oscurità
oscuro (Adjective) "dark"
12th cent. From Latin obscurus 'id.' From ob(s) "toward" (see ob-) and a fossil *scurus or *curus meaning "darkened." From Proto-Italic *skoi-ro- or *koi-ro- 'id.' If indeed related to Greek, Celtic and Gothic cognates, then from Proto-Indo-European *skoh2-i̯-ro- 'id.' From a root *skeh2- "to cover."
Indo-European
Romance
Portuguese obscuro, Galician escuro, Catalan obscur, French obscur, Italian oscuro, Eastern Vulgar Latin: Aromanian scur, Romanian obscur, Sardinian iscuru
Germanic
Gothic skeirs "bright," Old Norse skírr 'id.'
Hellenic
Ancient Greek σκίρον (skíron) "shady," meaning uncertain
-oso Adjective-forming suffix indicating an abundance or a bundle.
From Latin -osus, Old Latin -osos. From Proto-Italic *ōnt-to- 'id.' From Proto-Indo-European *o-u̯ont-to- 'id.'
Indo-European
Romance
Asturian -osu, Portuguese -oso, Catalan -ós, French -eux, Italian -oso, Aromanian -os, Romanian -os, Sardinian -oso
oso m. (Noun) "bear"
11th cent. From Latin ursus 'id.' From Proto-Italic *orsso- 'id.' From Proto-Indo-European *h2tḱo- 'id.'
Indo-European
Romance
Asturian osu, Portuguese usso, Galician oso, Catalan ós, French ours, Italian orso, Aromanian ursu, Romanian urs, Sardinian ursu
Celtic
Old Irish art "bear," "hero," Middle Welsh arth "bear," Old Breton Ard-, Arth- 'id.,' Gaulish Artio, bear goddess
Albanian
Albanian arí "bear"
Hellenic
Ancient Greek ἄρκτος (árktos) "bear"
Armenian
Armenian arǰ "bear"
Indo-Iranian
Sanskrit ŕ̥kṣa- "bear," Young Avestan arša 'id.'
As de Vaan (2014) points out, the word was heavily subjected to taboo distortion, as it was forbidden to speak the name of the bear during a hunt. Thus the word is phonologically warped. The appurtanance of Latin ursus is difficult to explain, Proto-Italic *orsso- should yield **orsus; furthermore, Proto-Italic *orsso- is difficult to explain because Proto-Indo-European *h2rtḱo- should yield **arsso-.
otorgar (Verb) "to authorize"
11th cent. From Vulgar Latin *auctoricare "to grant," from Latin auctorare 'id.,' derived from augere "to create," "to enlarge" (see aumento).
Indo-European
Romance
French octroyer, Italian otriare
otro (Adjective) "other," "another"
11th cent. Old Spanish otro. 10th cent. Old Spanish altro. Vulgar Latin alterum "other" (Peregrinatio, 4th cent.). From Latin alter "other" but also the ordinal number "second." From Proto-Italic *āl-tero- 'id.' From Proto-Indo-European *h2el- "other" and *-tero- "one of the two," a comparative suffix (see -tr-).
Indo-European
Romance
Asturian otru, Portuguese outro, Galician outro, Catalan altre, French autre, Italian altro, Aromanian altu, Romanian alt, Sardinian àteru
Italic
Oscan alttram "the other"
For further commentary on *h2el- see el (2), él, ella, ello.
-oy First person singular.
Old Spanish -o or . The explanation for the unexpected development from -o to -oy is unclear. The most probable theories are: contamination from yo (e.g. so yo > soy yo; do yo > doy yo) , Müller (1963); and (2) contamination from the now-extinct word y "there," which is known to be the origin of <y> in hay "there is" (see discussion and sources in Lloyd 1987).
oyente (Noun) "auditor"
15th cent. From oír.