Of things other than ships, 1630s. But oldest-recorded sense in English is "sheet of paper printed only on one side" (1570s). As an adverb by 1870; as an adjective by 1932. As a verb from 1930, "to skid sideways" (intransitive); transitive sense "to strike broadside, collide with the side of" is by 1970.
combining form used from 19c. to represent Latin latus "the side, flank of humans or animals, lateral surface," a word of uncertain origin. The Latin word also was used to express intimacy, attachment, or relationship via the notion of "attach to the side, at the side of."