hissing vs hushing

hissing and hushing both are nouns.

Word	Noun	Adjective	Verb	Adverb
hissing	Yes	No	No	No
hushing	Yes	No	No	No

As nouns, hissing and hushing are synonyms defined as:

hissing and hushing: a fricative sound (especially as an expression of disapproval)

Other synonyms of hissing include fizzle, hiss, sibilation.

hissing (noun)	hushing (noun)
a fricative sound (especially as an expression of disapproval)	a fricative sound (especially as an expression of disapproval)