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 PIE *dhe-mn, suffixed form of root *dhe- "to set, put." Meaning "school essay" is from 1540s. Extension to music first recorded 1670s; theme song first attested 1929. Theme park is from 1960.