best man(n = noun.person) - the principal groomsman at a wedding;
is a kind of groomsman
is a member of wedding, wedding party

N  friend, friend of one's bosom, alter ego, best friend, bosom friend, soulmate, fast friend, amicus, usque ad aras, fidus Achates, persona grata, acquaintance, neighbor, next-door neighbor, casual acquaintance, nodding acquaintance, wellwisher, favorer, fautor, patron, Mecaenas, tutelary saint, good genius, advocate, partisan, sympathizer, ally, friend in need, comrade, mate, companion, familiar, confrere, comrade, camarade, confidante, intimate, old crony, crony, chum, pal, buddy, bosom buddy, playfellow, playmate, childhood friend, bedfellow, bedmate, chamber fellow, associate, colleague, compeer, schoolmate, schoolfellow, classfellow, classman, classmate, roommate, fellow-man, stable companion, best man, maid of honor, matron of honor, compatriot, fellow countryman, countryman, shopmate, fellow-worker, shipmate, messmate, fellow companion, boon companion, pot companion, copartner, partner, senior partner, junior partner, Arcades ambo Pylades and Orestes Castor and Pollux, Nisus and Euryalus, Damon and Pythias, par nobile fratrum, host, Amphitryon, Boniface, guest, visitor, prot_eg_e, amici probantur rebus adversis, ohne bruder kann man leben nicht ohne Freund, best friend, my well-spring in the wilderness, conocidos muchos amigos pocos, friend more divine than all divinities, vida sin amigo muerte sin testigo.

N  marriage, matrimony, wedlock, union, intermarriage, miscegenation, the bonds of marriage, vinculum matrimonii, nuptial tie, married state, coverture, bed, cohabitation, match, betrothment, wedding, nuptials, Hymen, bridal, espousals, spousals, leading to the altar, nuptial benediction, epithalamium, sealing, torch of Hymen, temple of Hymen, hymeneal altar, honeymoon, bridesmaid, bridesman, best man, bride, bridegroom, married man, married woman, married couple, neogamist, Benedict, partner, spouse, mate, yokemate, husband, man, consort, baron, old man, good man, wife of one's bosom, helpmate, rib, better half, gray mare, old woman, old lady, good wife, goodwife, feme, feme coverte, squaw, lady, matron, matronage, matronhood, man and wife, wedded pair, Darby and Joan, spiritual wife, monogamy, bigamy, digamy, deuterogamy, trigamy, polygamy, mormonism, levirate, spiritual wifery, spiritual wifeism, polyandrism, Turk, bluebeard, unlawful marriage, left-handed marriage, morganatic marriage, ill- assorted marriage, mesalliance, mariage de convenance, marriage broker, matrimonial agency, matrimonial agent, matrimonial bureau, matchmaker, schatchen, married, one, one bone and one flesh, marriageable, nubile, engaged, betrothed, affianced, matrimonial, marital, conjugal, connubial, wedded, nuptial, hymeneal, spousal, bridal, the gray mare the better horse, a world-without-end bargain, marriages are made in Heaven, render me worthy of this noble wife, si qua voles apte nubere nube pari.

age of man, apron man, at best, at the best, average man, backup man, ballyhoo man, beef man, best, best and greatest, best evidence rule, best friend, best of all, best seller, best wishes, bionic man, black man, boskop man, broth of a man, c. h. best, career man, cave man, charles herbert best, city man, college man, common man, company man, con man, confidence man, conjure man, corner man, cow man, customer's man, dirty old man, divorced man, do one's best, elevator man, end man, enlisted man, ent man, fall of man, family man, fancy man, feral man, fighting man, fingerprint man, four-minute man, front man, g man, garbage man, gay man, get the best, gingerbread man, give one's best, government man, great man, had best, handy man, hatchet man, have the best, heidelberg man, hired man, hit man, holdup man, hollow man, holy man, honest man, inner man, iron man, isle of man, java man, ladies' man, leading man, learned man, leg man, level best, lookout man, maintenance man, man, man and wife, man eater, man eating, man friday, man hour, man in the street, man jack, man made, man of action, man of affairs, man of deeds, man of letters, man of means, man of science, man of the cloth, man of the world, married man, mechanical man, medical man, medicine man, middle-aged man, military man, miracle man, modern man, mountain man, muffin man, muscle man, navy man, neandertal man, neanderthal man, odd man out, odd-job man, old man, old man of the mountain, organization man, outdoor man, party man, peking man, piltdown man, pivot man, point man, poor man, pr man, preacher man, prehistoric man, property man, public relations man, publicity man, railroad man, railway man, red man, remittance man, renaissance man, rewrite man, rhodesian man, rich man, right hand man, right-hand man, second best, section man, service man, solo man, song and dance man, sporting man, squaw man, stan the man, stickup man, stone age man, straight man, straw man, strong man, stunt man, sunday best, t man, to a man, trigger man, trinil man, unmarried man, utility man, vigilance man, wealthy man, white man, wild man, wise man, wolf man, working man, worship of man, yellow man, yes man, young man