Guess/ɡes/ Definition 1 of 4Pro Tip 1/3Informal contexts Generally used in casual conversation, rather than in formal or academic situations. I guess they're not showing up. Pro Tip 2/3Express uncertainty Use 'guess' to indicate that you're not certain or when you lack full information. I guess it might rain later. Pro Tip 3/3Conversational filler Often serves as a softer way to start a sentence when you're unsure or trying to be polite. I guess I could make it to the party.