match

athletics, sport

battle, conflict, scrimmage, skirmish, struggle, tug-of-war, tussle

championship, national(s)

final, play-off, semifinal

derby, field day, open, outing

biathlon, decathlon, heptathlon, pentathlon, triathlon

marathon, race, ultramarathon

heat, round, run, set

rally, volley

round-robin, rubber, runoff, sudden death

dead heat, photo finish, seesaw

classic

monogamy

bigamy, polyandry, polygamy, polygyny

intermarriage, miscegenation, mixed marriage, remarriage

cohabitation, common-law marriage

civil union, domestic partnership

attachment, commitment, relationship

betrothal, engagement, espousal, hand, pledge, promise, proposal, troth

coordinate

coequal, counterpart, equal, equivalent, like, parallel, peer, rival

carbon copy, double, duplicate, facsimile, identical twin, likeness, mirror image, replica, ringer

analogue (or analog), similarity

analogue (or analog)

double, half, mate, twin

associate, colleague, companion, copartner, partner

competitor

effigy, portrait, portrayal

companion, fellow, mate

equal, equivalent

analogue (or analog), parallel

horse race, nail-biter

showdown

clash, collision, discord, friction

argument, controversy, debate, disagreement, disputation, dispute, dissension (also dissention), quarrel, row, wrangle

blend (with), conform (to), coordinate (with), go (with), harmonize (with)

complement, supplement

counterbalance, counterpoise

echo, image, mirror, repeat

add up (to), amount (to), approach, come (to), near

measure (up), partake (of), rival, suggest

commit, engage

affiance, betroth, pledge, promise

beat, better, eclipse, excel, outdistance, outdo, outshine, outstrip, overtop, surpass, top, transcend

amount (to), approach, touch

approximate, keep up, measure up (to), parallel, rival, stack up (against or with)