In the Navy, "XO" is short for this person
A person holding executive power... [DOC] [TLE] Naval Terminology L-Z - San Diego Navy History [PAR] Jun 11, 2005 ... (1) Any short line used as a handle or as a means for operating some piece of 
equipment; ... (1) Movement of a person, as "Lay aloft"; (2) to put something down
, as to lay title; (3) the direction of .... Ordinarily signed by the