The word solid describes something that holds its shape firmly rather than flowing like water or drifting like air. A rock is solid, water is liquid, and steam is gas. When you pick up a solid object like a book or a baseball, it doesn't change shape in your hands.

Solid also means strong and dependable. A solid friendship is one you can count on through good times and bad. A solid argument is well-reasoned and convincing, not flimsy or full of holes. When you give a solid performance in a play or game, you do consistently well without major mistakes.

In everyday conversation, people use solid to show approval: “That's a solid plan” means it's well thought out and likely to work. A solid student does reliable, quality work. A solid piece of furniture won't wobble or break easily.

The word can even describe facts: solid evidence is trustworthy and convincing, the kind that holds up under questioning. When someone asks if you're sure about something and you reply “I'm solid on that,” you're saying you're confident and certain, not wishy-washy or doubtful.