lock in vs shut up

lock in is not an adjective while shut up is an adjective.

Word	Noun	Adjective	Verb	Adverb
lock in	No	No	Yes	No
shut up	No	Yes	Yes	No

As verbs, lock in and shut up are synonyms defined as:

lock in and shut up: place in a place where something cannot be removed or someone cannot escape

Other synonyms of lock in include lock, lock away, lock up, put away, shut away.

lock in (adjective)	shut up (adjective)
	closely confined

lock in (verb)	shut up (verb)
place in a place where something cannot be removed or someone cannot escape	cause to be quiet or not talk
close with or as if with a tight seal	refuse to talk or stop talking; fall silent
	place in a place where something cannot be removed or someone cannot escape