inside: [16] Inside (a compound, of course, of in and side) was originally a noun, meaning ‘inner surface’ (‘Solomon builded the walls on the inside with Cedar timber’, Miles Coverdale’s translation of I Kings 6:15 1535), and it was not used as an adjective until the early 17th century – by Shakespeare, in fact. Adverbial and prepositional use are more recent still, from around the end of the 18th century. => side[inside etymology, inside origin, 英语词源]