REUS, civil law. This word has two different meanings. 1. A party to a suit, whether plaintiff or defendant; Reus est qui cum altero litem contestatem habet, sive legit, sive cum eo adum est. 2. A party to a contract; reus credendi is be to whom something is due, by whatever title it may be; reus debendi is he who owes, for whatever cause. Poth. Pand. lib. 50, h. t.