WordNet sense 1 (the cardinal number that is the sum of one and one and one):

ternary, three, trey, triad, trinity, trio, triplet, troika, deuce-ace, III, tercet, ternion, terzetto, tierce, trine

WordNet sense 2 (restraint consisting of a rope (or light chain) used to restrain an animal):

lead, tether, lead, lead

WordNet sense 3 (fasten with a rope):

rope

WordNet sense 4 (a figurative restraint):

collar