Where does the term "law suit" for a legal case come from? It seems to perhaps only be used to refer to civil cases, however. Also, is it a purely American (USA) term or does it also find use elsewhere?
The historical root is Old French sieute, sivre meaning "follow, pursue". You pursue your defendant in court. This is an ordinary legal term in post-Norman England. The root is also invoked every time the government prosecutes a person for a crime. The expression "law suit" is more modern, being a rearrangement of "suit at law". An early attestation in the legal sense is (1325) Statutes of Realm (Rawl. B.520) (2011) v. 6
Ant ȝif a ne cometh noȝt, þanne a sullen ben iiuged ase for ateint, ant sullen ȝelde duble, þoru þe siwte of þe king, to hoem þat habbeth ihaued þene harm.