late-onset

The compound 'late-onset' is a modern English formation, primarily used in medical and psychological contexts. Its first element, 'late', traces back to a Proto-Germanic root meaning 'slow' or 'sluggish', which evolved to denote something happening after the expected or usual time. The second element, 'onset', is a straightforward combination of the preposition 'on' and the verb 'set', literally meaning 'a setting on' or 'an attack upon', which broadened to signify the initial stage of any event. The term's logic is transparently literal: a 'late beginning' describes conditions that manifest significantly later in life than is typical, distinguishing them from congenital or early-developing forms.

Structure: late (occurring after the usual time) + onset (beginning) - late: From Old English læt (slow, tardy), of Germanic origin. Functions as an adjective modifying the noun 'onset' to specify its timing. - onset: From the phrase 'on set', from Old English on + settan (to set). Functions as a noun meaning the beginning or start of something.