Final answer:
The 8-letter word for eavesdropping is 'overhear'.
Step-by-step explanation:
The 8-letter word for what you do when you eavesdrop is overhear, option a. To overhear means to unintentionally listen to someone's conversation without their knowledge or consent. It can happen accidentally or deliberately, but it is generally considered a breach of privacy. For example, if you are sitting in a coffee shop and hear a conversation at the next table, you are overhearing their conversation.