To cozen is to mislead, defraud, or fool someone through lies. Cozen rhymes with dozen, and if you say you had two wrong answers on your math test, but you really had a dozen, you might be trying to cozen your parents.
While not related in roots, the first part of cozen sounds like the slang word "cuz." If someone asks why you lied, you might say "Cuz I didn't want you to know the truth." And to cozen is to keep the truth hidden and deceive or cheat. Using a trick to get something is one way to cozen, and if you tell a partial truth, there's still a part lie or an attempt to cozen and mislead.