hirer comes from hire (Old English hȳrian 'to engage for wages', from hȳr 'wages') + the agent suffix -er. Morphologically, the ending is part of the etymology: the suffix is attached to the older base named in the history, producing a later English derivative. In present English, the noun sense is "a person who hires or employs another, or who rents something", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as hire and hireling. Its semantic neighborhood includes employer, renter, lessee, and engager, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Old English hȳrian and Proto-Germanic *hūzijaną.