WordNet sense 1 (the molecular weight of a substance expressed in grams; the basic unit of amount of substance adopted under the Systeme International d'Unites):

mol, gram molecule

WordNet sense 2 (a spy who works against enemy espionage):

counterspy

WordNet sense 3 (a protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away):

breakwater, bulwark, groin, jetty, seawall, groyne