In the phrase, pro and con, for and against, con denotes the negative side of a question. As a noun, a person who is in the negative; as the pros and cons.

To know. I conne no skill. I shall not conne answer. I shall not know or be able to answer.

To make ones self master of; to fix in the mend or commit to memory; as, to con a lesson. To con thanks, to be pleased or obliged, or to thank.