Ironclad/ˈaɪərnklæd/ Definition 1 of 3Pro Tip 1/2Beyond Dispute Use 'ironclad' to describe something so certain that it cannot be questioned. His alibi was ironclad; the jury believed him instantly. Pro Tip 2/2Strong Assurance 'Ironclad' can express a guarantee or promise deemed extremely reliable. The store's ironclad return policy made customers feel confident.