to seal: to press a seal onto something in order to authorize it, secure it shut, or close it off
In the ancient world a seal was a personal mark, cut into a ring or a small stone, that a person pressed into soft clay or wax. It stood for the owner the way a signature does today, and once it was set, breaking it without leaving a trace was nearly impossible. This one verb covers the whole act of setting that seal, and its senses fan out from there.
At its most concrete the word means to make a document official: a deed, a letter, or a royal decree was sealed so that everyone knew it was genuine and binding. From that it stretches to sealing something up so it stays closed and safe, whether to keep it secret, to preserve it until the right time, or simply to shut it tight. In its strongest figures it means to close something off completely, so that stars do not shine, a hand cannot work, or a spring cannot be reached.
The thread running through all of these is a sealed thing that no one may tamper with. Whether the point is authority, secrecy, or sheer closure depends on what is being sealed and why.
Nuances
Whether the word in Ezekiel 28:12 is this verb ("you seal up the pattern of perfection," its full measure) or a closely spelled noun meaning "signet, seal" ("you were the signet of perfection").
- minorityIt is the verb "to seal": the figure of Tyre's king sets the finishing seal on a perfect design, sealing up its full measure.; BDB, s.v. חתם
- majorityThe consonants should be read as the noun "signet, seal," giving "you were the signet of perfection."; W. Zimmerli, Ezekiel 2 (Hermeneia); HALOT, s.v. חוֹתָם