horse (an equid) / a coarse, rude man / knight / heroin / horsepower (a unit that measures the power of an engine)

sea horse

horsepower (non-metric unit of power) / horsepower (metric unit of power)

ponytail

(Brazil) pommel horse

(rare) horsepower (metric)

hobby horse (a child's toy consisting of a (usually wooden or cloth) horse's head mounted on a stick) / a skidding U-turn with a vehicle

(Greek mythology) Trojan horse (wooden horse used by the Greeks to infiltrate Troy) / (by extension) Trojan horse (something which looks innocent placed among the enemy) / (computing) Trojan horse; Trojan (malicious program disguised as legitimate software)

Superseded spelling of cavalo de Troia. (used in Brazil until 2015).

(informal) back door (subsidiary entrance to building)