The Oxford Thesaurus An A-Z Dictionary of Synonyms INTRO ...

underflow: Caught in the undercurrent, he was carried out to
sea. 2 undertone, subcurrent, trend, tendency, overtone, tenor,
suggestion, murmur, implication, connotation, sense, feeling,
aura, tinge, flavour, atmosphere, ambience or ambiance;
vibrations, Colloq vibes: There is a sinister undercurrent of
gloom about this place.
undercut v. 1 undermine, excavate, hollow out, cut out or away, gouge
out: If you undercut the roadway it will collapse. 2
underprice, undercharge, sacrifice, sell cheaply or at a loss,
undersell: The supermarkets undercut prices and put the
independent grocers out of business.
underdog n. loser, scapegoat, victim; vanquished, defenceless; Colloq
fall guy, little fellow or guy: It has always been our policy
to fight for the underdog.
underestimate
v. undervalue, underrate, discount, misjudge, miscalculate,
misprize, minimize, depreciate, belittle, not do justice to,
fail to appreciate, set (too) little store by, think (too)
little of: No one should underestimate the physical and mental
effort involved.
undergo v. suffer, bear, endure, experience, live or go through, be
subjected to, subject oneself to, sustain, submit to, weather,
stand, withstand: The hotel has recently undergone extensive
refurbishing.
underground
adj. 1 subterranean, buried, below-ground, sunken, covered:
They crept through the underground passage into the treasure
room. 2 secret, clandestine, concealed, hidden, covert,
undercover, surreptitious, stealthy, private: The secret
service has a worldwide underground network of agents. 3
alternative, radical, experimental, avant-garde, nonconformist,
revolutionary: Some underground newspapers that sprang up in
the 1960s are still being published.
--n. 4 tube, metro, underground railway, US subway: Two more
stops on the underground and we'll be there. 5 resistance,
partisans or partizans, freedom fighters, (in France) Maquis,
insurgents, seditionaries or seditionists, insurrectionists,