compulsory, a. constraining, coercive, obligatory, unavoidable.  Antonyms:  optional, discretional, elective.

compunction, n. qualm, contrition, remorse, regret, sting of conscience.

compute, v. reckon, calculate, enumerate, rate, estimate.

comrade, n. associate, companion, mate, compeer.

comradeship, n. association, camaraderie.

concave, a. rounded, vaulted.  Antonym:  convex.

concealed, a. hidden, latent, secreted, clandestine, disguised.

concealment, n. secretion, hiding; secrecy, latency, privacy, seclusion, retirement; suppression.

conceit, n. idea, conception, fancy; whim, caprice, vagary, freak; priggery, vanity, egotism, self-conceit, inflation, self-glorification, overweening, conceitedness.

conceited, a. egotistical, priggish, bombastic, bumptious, vain, overweening, self-conceited.

concentrate, v. centralize, focus, consolidate; condense, rectify.

concentration, n. centralization, consolidation; condensation.

concept, n. conception, notion, idea.

conception, n. ideation, imagination; idea, concept, notion, impression.

concern, n. business, affair; moment, importance, interest, weight, consequence; solicitude, anxiety, uneasiness care; firm, house, company, partnership.  Antonyms:  unconcern, inconsequence.

concerned, a. solicitous, worried, anxious, apprehensive, troubled, uneasy.  Antonyms:  unconcerned, indifferent.

concerning, prep. regarding, about, respecting, touching, with reference to.

concert, n. accordance, concurrence, harmony; musicale.

concise, a. epigrammatic, sententious, succinct, laconic, pithy.  Antonyms:  diffuse, prolix.

conclude, v. decide, determine, resolve; end, close; infer, deduce; effect, arrange.

conclusion, n. decision, determination; inference, deduction, corollary, illation; close, end, peroration, finale, completion, denouement, l’envoy.

concoct, v. compound, mix; devise, contrive, invent, excogitate.

concrete, a. solidified, consolidated; specific, special, particular.

concretion, n. solidification, lapidescence, stone; clot, coagulation.

concubine, n. paramour, odalisque; pl. harem, seraglio.

condemn, v. denounce, anathematize, curse, execrate, reprobate, doom, ban.  Antonyms:  exonerate, exculpate, vindicate, absolve, justify, praise.

condemnation, n. denunciation, reprobation, execration, ban.

condemnatory, a. denunciatory, condemning.

condense, v. abridge, epitomize, reduce; compress, concentrate.

condescend, v. deign, vouchsafe.

condition, n. state, plight, category, predicament, situation, stipulation, provision, proviso, term, prerequisite.

conditional, a. contingent, subject, provisory.

conduce, v. lead, tend, contribute, redound, subserve, advance.