consilium

Consilium, consilii, n., second declension, from consulo. Three senses English keeps apart: a plan or purpose, the advice somebody gives, and the body that gives it. Consilium capere or inire is to form a plan, consilium dare is to advise, and consilium habere is to hold a council.

The real hazard is its neighbour concilium, "an assembly called together", from concilio. One letter apart, and medieval scribes swapped them constantly, so church councils turn up under both spellings in manuscripts. English preserves exactly the same trap in counsel and council, which is either a comfort or a warning. Also from this root: consul, consultum, and English consult, counsellor and, through French, conseil.