knuckler vs knuckleball

knuckler and knuckleball both are nouns.

Word	Noun	Adjective	Verb	Adverb
knuckler	Yes	No	No	No
knuckleball	Yes	No	No	No

As nouns, knuckler and knuckleball are synonyms defined as:

knuckler and knuckleball: a baseball pitch thrown with little speed or spin

knuckler (noun)	knuckleball (noun)
a baseball pitch thrown with little speed or spin	a baseball pitch thrown with little speed or spin