consul

Consul, consulis is third declension masculine. Two were elected each year and the year itself was named after them, which is why dates in Latin prose come as an ablative absolute with no verb at all: Caesare et Bibulo consulibus, "in the consulship of Caesar and Bibulus". Learn that construction cold, because it appears constantly and there is nothing in it to parse your way into.

The office is the consulatus, the adjective consularis, and a former holder a vir consularis. English kept the word and lost the job: a modern consul stamps visas rather than commanding two legions.