(adj) not given enough food to eat
underfed
(adj, adv) located or occurring below the surface of the earth
underground
(prep) below something; on the bottom side of something
underneath
(n) the area beneath the arm at the shoulder; (adj) placed at or along the armpit
underarm
(n) plants, bushes, and small trees growing under larger trees in a forest
underbrush
under-
too little; below