Antonyms are words that have opposite meanings to a particular word. For "give the green light," the antonyms could be "deny permission," "prohibit," "veto," "refuse approval" or "disapprove." These words indicate a refusal to grant permission, approval or support for a certain action or decision. Each of these opposite meanings could thoroughly disrupt or halt any forward movement in a project or plan. In contrast, "give the green light" means to provide permission, the go-ahead or approval to proceed. Knowing the antonyms of a word can help in understanding context, as well as choosing the right word to use for a particular situation.