Merriam-Webster's Dictionary and Thesaurus - Merriam-Webster [1464]
un·der·age adjective : of less than mature or legal age
un·der·arm adjective 1 : UNDERHAND 2 2 : placed under or on the underside of the arms <~ seams> — underarm adverb or noun un·der·bel·ly noun 1 : the underside of a body or mass 2 : a vulnerable area Synonyms bottom, underside—more at BOTTOM un·der·bid verb -bid; -bid·ding 1 : to bid less than another 2 : to bid too low un·der·body noun : the lower parts of the body of a vehicle un·der·bred adjective : marked by lack of good breeding un·der·brush noun : shrubs, bushes, or small trees growing beneath large trees un·der·car·riage noun 1 : a supporting framework (as of an automobile) 2 : the landing gear of an airplane un·der·charge verb : to charge (as a person) too little — undercharge noun un·der·class noun : LOWER CLASS un·der·class·man noun : a member of the freshman or sophomore class un·der·clothes noun plural : UNDERWEAR un·der·cloth·ing noun : clothing or an article of clothing worn next to the skin and under other clothing : UNDERWEAR un·der·coat noun 1 : a coat worn under another 2 : a growth of short hair or fur partly concealed by the longer and usu. coarser hairs of a mammal 3 : a coat of paint under another un·der·coat·ing noun : a special waterproof coating applied to the underside of a vehicle un·der·cov·er adjective : acting or executed in secret; especially : employed or engaged in secret investigation Synonyms clandestine, covert, furtive, hugger-mugger, private, secret, sneak, sneaky, stealthy, surreptitious, underground, underhanded—more at SECRET un·der·croft noun [ORIGIN: ME, fr. under + crofte crypt, fr. MD, fr. ML crupta, fr. L crypta] : a vaulted chamber under a church un·der·cur·rent noun 1 : a current below the surface 2 : a hidden tendency of feeling or opinion un·der·cut verb -cut; -cut·ting 1 : to cut away the underpart of 2 : to offer to sell or to work at a lower rate than 3 : to strike (the ball) obliquely downward so as to give a backward spin or elevation to the shot — un·der·cut noun un·der·de·vel·oped adjective 1 : not normally or adequately developed <~ muscles> 2 : having a relatively low level of economic development un·der·dog noun : the loser or predicted loser in a struggle un·der·done adjective : not thoroughly done or cooked : RARE un·der·draw·ers noun plural : UNDERPANTS un·der·em·pha·size verb : to emphasize inadequately — un·der·em·pha·sis noun un·der·em·ployed adjective : having less than full-time or adequate employment un·der·es·ti·mate verb : to set too low a value on un·der·ex·pose verb : to expose (a photographic plate or film) for less time than is needed — un·der·ex·po·sure noun un·der·feed verb -fed ; -feed·ing : to feed with too little food un·der·foot adverb 1 : under the feet 2 : close about one's feet : in the way un·der·fur noun : an undercoat of fur esp. when thick and soft un·der·gar·ment noun : a garment to be worn under another un·der·gird verb : to brace up : STRENGTHEN un·der·go verb -went ; -gone ; -go·ing 1 : to submit to : ENDURE 2 : to go through : EXPERIENCE Synonyms endure, experience, feel, have, know, see, suffer, sustain, taste—more at EXPERIENCE un·der·grad noun : UNDERGRADUATE un·der·grad·u·ate noun : a student at a university or college who has not taken a first degree 1underground adverb 1 : beneath the surface of the earth 2 : in or into hiding or secret operation 2underground noun 1 : a space under the surface of the ground; especially : SUBWAY 2 : a secret political movement or group; especially : an organized body working in secret to overthrow a government or an occupying power 3 : an avant-garde group or movement that operates outside the establishment 3underground adjective 1 : being, growing, operating, or located below the surface of the ground <~ stems> 2 : conducted by secret means 3 :