1. [Unix: from execute] Synonym for chain, derives from the exec(2) call.
2. [from executive] obs. The command interpreter for an OS (see shell); term esp. used around mainframes, and prob.: derived from UNIVAC's archaic EXEC 2 and EXEC 8 operating systems.
3. At IBM and VM/CMS shops, the equivalent of a shell command file (among VM/CMS users).
The mainstream ‘exec’ as an abbreviation for (human) executive is not used. To a hacker, an ‘exec’ is always a program, never a person.