The coded instruction a living thing is built from and passes on. Also, by extension, the essential character a thing inherits.
Assembled in the twentieth century from deoxy- (Greek, without oxygen), ribose (a coined sugar name, itself built from an anagram of arabinose), and nucleic (from Latin nucleus, kernel); shortened to the initials DNA for the molecule that carries what a living thing passes on.
The coded instruction a living thing is built from and hands onward, and by extension the essential character something inherits without choosing it. What a system calls its DNA is the part of it too basic to be optional.