fee splitting vs defrayment

fee splitting and defrayment both are nouns.

Word	Noun	Adjective	Verb	Adverb
fee splitting	Yes	No	No	No
defrayment	Yes	No	No	No

As nouns, defrayment is a hypernym of fee splitting; that is, defrayment is a word with a broader meaning than fee splitting:

fee splitting: payment (usually by doctors or lawyers) of part of the fee in return for the referral
defrayment: the act of paying money

Other hypernyms of fee splitting include defrayal, payment.

fee splitting (noun)	defrayment (noun)
payment (usually by doctors or lawyers) of part of the fee in return for the referral	the act of paying money