safecracker vs thief

safecracker and thief both are nouns.

Word	Noun	Adjective	Verb	Adverb
safecracker	Yes	No	No	No
thief	Yes	No	No	No

As nouns, thief is a hypernym of safecracker; that is, thief is a word with a broader meaning than safecracker:

safecracker: a thief who breaks open safes to steal valuable contents
thief: a criminal who takes property belonging to someone else with the intention of keeping it or selling it

Other hypernyms of safecracker include stealer.

safecracker (noun)	thief (noun)
a thief who breaks open safes to steal valuable contents	a criminal who takes property belonging to someone else with the intention of keeping it or selling it