"one who has the authority or power to command or order," early 14c., comandur, from Old French comandeor "commander, commandant," from comander "to order, enjoin" (see command (v.)). Commander in chief "commander of all the armies of a state" is attested from 1650s. In the U.S., by the Constitution, it is the president; George Washington was so called by 1778.
late 15c., "ruling, controlling, directing with authority, of great or controlling importance," present-participle adjective from command (v.). Meaning "nobly dignified, compelling respect, characteristic of one fitted for command" is from 1590s. Meaning "dominant by virtue of size or position" is from 1630s. Related: Commandingly (mid-15c.) "imperiously."