A more thorough explanation:

fiancer (fyahn-say), vb. [Law French] To pledge one's faith.

Fiancer is a verb that comes from the Law French language. It means to promise or pledge one's faith to someone. This word is often used in the context of engagement, where two people promise to marry each other and pledge their faithfulness to each other.

Example 1: John fianced Mary and promised to marry her next year.

Example 2: Sarah and Tom fianced each other and exchanged rings as a symbol of their commitment.

These examples illustrate how fiancer is used in the context of engagement. In both examples, two people promise to marry each other and pledge their faithfulness to each other. The word fiancer is used to describe this act of pledging one's faith, which is an important part of the engagement process.