I finally found a site with falconry vocabulary. It confirmed definition of tercel meaning male a third smaller.
Words worth looking up: Bate, Bell, Bewit,Creance, Eyass, Feak, Haggard, Hood, Imp, Imprint, Jess, Mantle, Pellet, Sharp Set, Stoop, Tercel, Yarak

http://www.wingmasters.net/lofalconry.htm