waistline vs waist

waistline and waist both are nouns.

Word	Noun	Adjective	Verb	Adverb
waistline	Yes	No	No	No
waist	Yes	No	No	No

As nouns, waistline and waist are synonyms defined as:

waistline and waist: the narrowing of the body between the ribs and hips

waistline (noun)	waist (noun)
the narrowing of the body between the ribs and hips	the narrow part of the shoe connecting the heel and the wide part of the sole
	the narrowing of the body between the ribs and hips