Transferred use of the mainly Scottish surname, in origin a local name for someone who came ‘from the island’ (Anglo-Norman de l'isle). (The island in question would in many cases have been an area of higher, dry ground in a marsh or fen, rather than in a sea or river.) There may have been some confusion with Lyall.
English: habitational name from the city of Chichester in Sussex, probably named with the Old English personal name Cissa + Old English ceaster ‘Roman fort’. (Cissa is attested as the name of a historical person; it is of uncertain etymology.) Alternatively, the first element may be an Old English word cisse ‘gravelly feature’. The name is also established in Ireland.