The only free and comprehensive online etymological dictionary of the Spanish language
imagen f. (Noun) "image"

13th cent. From Latin imaginem, accusative of imago 'id.' Derived from a verb in Proto-Italic *imā-je/o- "to copy," itself a verb derived from an earlier noun in Proto-Indo-European *h2im-h2 "copy," "image." The root *h2em- is of unknown meaning, perhaps "to double," "to reproduce."

Romance: Western Vulgar Latin: Portuguese imagem, Catalan imatge, French image, Italian immagine; Eastern Vulgar Latin: Romanian imagine

Indo-European: Anatolian: Hittite ḫimma- "imitation," "replica"
imaginar (Verb) "to imagine"

14th cent. From Latin imaginari 'id.,' from imago "image" (see imagen).

Romance: Western Vulgar Latin: French imaginer
imbécil (Adjective; Noun) "moronic;" "imbecile"

16th cent. Old Spanish imbecil (with stress on -íl). Borrowed from Latin imbeccilus "weak," but literally "without one's staff." From im- "not" (see in-) and baculum "staff" (see báculo).
implicar (Verb) "to implicate"

From Latin implicare "to implicate," "to fold (in);" from in- "in" (see in-) and plicare "to fold" (see llegar).

Romance: Western Vulgar Latin: Portuguese implicar, Galician implicar, Catalan implicar, French impliquer, Italian implicare; Eastern Vulgar Latin: Romanian implica
importante (Adjective) "important"

From Latin importare "to matter" (see importar).

Romance: Western Vulgar Latin: Portuguese importar, Catalan importar, French importer, Italian importare
importar (Verb) "to matter," "to be important;" "to import"

From Latin importare 'id.,' from im- (see en-) and portare "to carry" (see portar).

Romance: Western Vulgar Latin: Portuguese importar, Catalan importar, French importer, Italian importare
imposible (Adjective) "impossible"

From Latin impossibilis 'id.,' from in- "not" (see in-) and possibilis "possible" (see posible).
impulso m. (Noun) "impulse"

Late 15th cent. From Latin impulsus 'id.,' from impellere "to push against," "to incite." From in- "in" (see in-) and pellare "to drive" (see pulso).
in- (1), im- A negation prefix indicating "not" or "against."

From Latin in- 'id.' From Proto-Italic *in- 'id.' From Proto-Indo-European *n̥- 'id.'

Italic: Oscan an-, Umbrian a-

Indo-European: Celtic: Old Irish in-, Old Welsh an-, Old Breton an-, Old Cornish an-; Germanic: Gothic un-, Old Norse ó-, Old High German un-, Old Saxon un-, Old English un- (English un-); Hellenic: Ancient Greek ἀν- (án-); Indo-Iranian: Sanskrit an-, Avestan a-; Tocharian: A an-, B an-
in- (2), en- Prefix "in," "into"

A prefix grammaticized from the Latin preposition in 'id.' See en.

Italic: Oscan en, Paelignian i

Indo-European: Celtic: Old Irish i, Old Welsh in, Old Breton en, Cornish yn; Germanic: Gothic in, Old Norse í, Old Saxon in, Old High German in, Old English in (English in); Balto-Slavic: Old Church Slavonic vъn, Russian vo, Lithuanian į, Old Prussian en; Hellenic: Ancient Greek ἐν (en); Armenian: i; Tocharian: A yn-, B in-

Also im- (e.g. importar) which occurs in words borrowed from Latin, rather than natively inherited.