falling off vs falloff

falling off and falloff both are nouns.

Word	Noun	Adjective	Verb	Adverb
falling off	Yes	No	No	No
falloff	Yes	No	No	No

As nouns, falling off and falloff are synonyms defined as:

falling off and falloff: a noticeable deterioration in performance or quality

Other synonyms of falling off include drop-off, slack, slump.

falling off (noun)	falloff (noun)
a noticeable deterioration in performance or quality	a noticeable deterioration in performance or quality