The only free and comprehensive online etymological dictionary of the Spanish language
inmediato (Adjective) "immediate"

From Late Latin immediatus 'id.' From in- "in" (see in- (2)) and mediatus "halved by the middle," "divided in twain" (see mediar).

Romance: Western Vulgar Latin: Portuguese imediato, Catalan immediat, French immédiat, Italian immediato
inocente (Adjective) "innocent"

From Latin innocentem, accusative of innocens 'id.' From in- "not" (see in- (1)) and nocens "wicked," "harmful" (see nocente).

Romance: Western Vulgar Latin: Portuguese inocente, French innocent, Italian innocente; Eastern Vulgar Latin: Romanian inocent
inteligente (Adjective) "intelligent"

Very early 17th cent. From Latin intellegentem, accusative of intellegens 'id.' From inter- "between" (see inter-) and legere "to read" (see leer).
intentar (Verb) "to try"

From Latin intentar "to extend toward," from intendere "to focus on," "to strain" (see entender) and frequentive suffix -tare (see note under faltar).

Romance: Western Vulgar Latin: Asturian entender, Portuguese intender, Catalan entendre, French entendre, Italian intendere; Eastern Vulgar Latin: Aromanian ntindu, Romanian întinde; Sardinian: intèndhere
intento m. (Noun) "attempt"

Meaning influenced by Medieval Latin intentus "attempt." From Latin intentus "extension;" itself from intentare "to extend towards" (see intentar).
inter- (Prefix) "between"

From Latin inter- 'id.' Akin to English inter-, which was borrowed from the Latin. Originally a preposition inter (see entre).
interesante (Adjective) "interesting"

17th cent. From interesar.
interesar (Verb) "to interest"

17th cent. From Medieval Latin interesse "involvement," from Latin interesse "involvement" but originally "to be between." From inter- and esse "to be" (see entre and ser).
ínterin m. (Noun, Adverb) "interim," "meanwhile"

From Latin interim 'id.' From inter "between" (see entre) and -im, "toward that" (accusative of is, see éste).
interior m. (Adjective, Noun) "interior"

15th cent. An adjectival from Latin interior 'id.' From Proto-Italic *n̥tero- 'id.' From Proto-Indo-European *h1én-tero- 'id.,' a compound of *h1en "in" (whence en) and *-tero-, a comparative suffix (see -tr-).

Indo-European: Hellenic: Ancient Greek ἔντερα (éntera) "intestines;" Armenian: ənderk' "entrails;" Indo-Iranian: Sanskrit ántara- "interior," Young Avestan aṇtara- 'id.'