Definition of seal verb from the Oxford Advanced Learner's Dictionary

Oxford3000

seal

verb
siːl
 
; siːl
 
 
 

close envelope

1 seal something (up/down) to close an envelope, etc. by sticking the edges of the opening togetherMake sure you've signed the cheque before sealing the envelope.a sealed bid(= one that is kept in a sealed envelope and therefore remains secret until all other bids have been received)
 

close container

2 [often passive] seal something (up) (with something) to close a container tightly or fill a crack, etc, especially so that air, liquid, etc. cannot get in or outThe organs are kept in sealed plastic bags.
 

cover surface

3 [often passive] seal something (with something) to cover the surface of something with a substance in order to protect itThe floors had been stripped and sealed with varnish.
 

make something definite

4 seal something to make something definite, so that it cannot be changed or argued aboutto seal a contractThey drank a glass of wine to seal their new friendship.The discovery of new evidence sealed his fate(= nothing could prevent what was going to happen to him).She sealed victory with a birdie at the final hole.
 

close borders/exits

5 seal something (of the police, army, etc.) to prevent people from passing through a placeTroops have sealed the borders between the countries.
Idioms
see
my lips are sealed at lip
, signed and sealedsigned, sealed and delivered at sign v.
Phrasal verbs

seal something in

to prevent something that is contained in something else from escapingFold the pastry over at the ends to seal in the juices.

seal something in something

to put something in an envelope, container, etc. and seal itThe body was sealed in a lead coffin.

seal something off

(of the police, army) to prevent people from entering a particular areaTroops sealed off the site following a bomb alert.The road will remain sealed off until the police have completed their investigations.