To broach a topic is to bring it up for discussion: Now is the time to broach the subject. As a verb, broach also means "to open or enlarge a hole." The noun broach refers to a pointed tool which performs that operation.
A brooch, a decorative pin or clip, is nothing like a broach. But since they're often pronounced alike, and because ignorance never rests, some dictionaries accept broach as an alternative spelling of brooch.