The only free and comprehensive online etymological dictionary of the Spanish language
in- (2), en- Prefix "in," "into"
A prefix grammaticized from the Latin preposition in 'id.' See en.
Indo-European
Italic
Oscan en, Paelignian i
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
Armenian i
Tocharian
A yn-, B in-

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