macies

The root macies comes from Latin maciēs, 'leanness, thinness, a wasting away,' closely tied to the adjective macer, 'thin, lean, meager.' (That same macer, by a separate path, gives us meager — stingy, scanty, lean.) At its heart, macies is the look of a body that has been worn down to skin and bone.

In English this is an unusually narrow root: it lives almost entirely inside one word and its forms — emaciate. The build is simple. The prefix e- (a reduced form of ex-, 'out') attaches to the maci- stem and an -ate verb ending: e- + maci + -ate. Literally it is 'to make thin out,' to waste away until the leanness shows. The e- here works like an intensifier — not 'thin' but 'thinned right out,' down to a gaunt, hollow state.

From the verb emaciate come the two forms you will actually meet most. The past participle emaciated has hardened into an adjective — it is by far the most common member — describing someone shockingly thin from illness, hunger, or hardship (an emaciated prisoner, an emaciated stray dog). The noun emaciation names the condition itself, the state of being wasted away, and shows up mostly in medical and clinical writing.

This is a good example of a root that is real but tiny. There is no large family to map, no clever prefix system to play with. The whole value of macies is recognizing one vivid image — wasting thinness — locked inside emaciated, so the word stops looking arbitrary and starts looking like exactly what it means.