The only free and comprehensive online etymological dictionary of the Spanish language
-ico Adjective-forming suffix
From Latin -icus 'id.' From Proto-Italic *-īko-, a decausative suffix deriving from the instrumental suffix in Proto-Indo-European *-i̯h1-ko-.
An uncommon variant -eco reflects i ~ e confusion in Vulgar Latin in Iberia.
Indo-European
Romance
Asturian -icu, Portuguese -ico, Galician -ico, Catalan -ic, French -ique, Italian -ico, Aromanian -ic
Balto-Slavic
Old Church Slavonic -ъkъ
Hellenic
Ancient Greek -ικός (ikós)
Indo-Iranian
Sanskrit -śas