margin of safety vs safety margin

margin of safety and safety margin both are nouns.

Word	Noun	Adjective	Verb	Adverb
margin of safety	Yes	No	No	No
safety margin	Yes	No	No	No

As nouns, margin of safety and safety margin are synonyms defined as:

margin of safety and safety margin: the margin required in order to insure safety

Other synonyms of margin of safety include margin of error.

margin of safety (noun)	safety margin (noun)
the margin required in order to insure safety	the margin required in order to insure safety