theme (n.)
early 14c., "subject or topic on which a person writes or speaks," from Old French tesme (13c., with silent -s- "indicating vowel length" [OED], Modern French thème) and directly from Latin thema "a subject, thesis," from Greek thema "a proposition, subject, deposit," literally "something set down," from root of tithenai "put down, place," from PIE *dhe-mn, from root *dhe- "to put, to do" (see factitious). Meaning "school essay" is from 1540s. Extension to music first recorded 1670s; theme song first attested 1929. Theme park is from 1960.