Jesus is Rex, Lex, Lux, Dux

Antique REX, LEX, LUX, DUX pendant
The meaning of this unusual late 19th century pendant cross is at first unclear, and had not been worked out by the dealer I bought it from. From my grammar school education, I knew that Rex,Lex,Lux,Dux is Latin, and can be taken to have a Christian meaning ''My King, My Law, My Light,

My Leader'' and appears in various arrangements of the words as the motto of several American colleges - Yale, Talladega College, Alabama, Idaho College, and The Order of St Luke the Physician.
Whatever the arrangement of the words, they centre on ''X'' the Greek ''Chi'' the first letter of Christ''s name in Greek.

Xmas is a common abbreviation of the word Christmas. ... The "X" comes from the Greek letter Chi, which is the first letter of the Greek word Χριστός, which in English is "Christ".

The "-mas" part is from the Latin-derived Old English word for Mass.