The Collaborative International Dictionary of English v.0.48:
Thereon \There*on"\, adv. [AS. ??ron. See There, and On.] On that or this. --Chaucer. [1913 Webster] Then the king said, Hang him thereon. --Esther vii. 9. [1913 Webster]WordNet (r) 3.0 (2006):
thereon adv 1: on that; "text and commentary thereon" [syn: thereon, on it, on that]