1 symbol, token, mark, insigne (pl. insignia), sign, signet, crest, bearing, coat of arms, escutcheon, emblem, badge, monogram, identification, cartouche, design, imprint, stamp:
The seal on his ring showed a crouching lion.
2 authentication, confirmation, verification, validation, affirmation, attestation, ratification, corroboration, assurance, guarantee or guaranty, endorsement, substantiation, evidence, notice, notification:
Management set their seal of approval on the plans.
3 Sometimes, seal off or up. close (off or up), shut (off), zip up, plug (up), stop (up), lock, bolt, secure, batten down, make airtight or waterproof; cork:
All exits had been sealed off. They sealed up the windows so that no air could get in
4 authenticate, confirm, verify, validate, affirm, attest, ratify, clinch, corroborate, assure, ensure, guarantee, endorse:
The peace treaty was sealed by the marriage of the king to the emperor's daughter.