Rex /reks/ BrE AmE noun British English
[ Date: 1600-1700 ; Language: Latin ; Origin: 'king' ]
1 . a title used in official writing after the name of a king, when the king’s name has been written in Latin:
Henricus Rex (=King Henry)
2 . law a word meaning the state, used in the names of law cases in Britain when a king is ruling ⇨ regina :
Rex v Jones