to a fault vs excessively

to a fault and excessively both are adverbs.

Word	Noun	Adjective	Verb	Adverb
to a fault	No	No	No	Yes
excessively	No	No	No	Yes

As adverbs, to a fault and excessively are synonyms defined as:

to a fault and excessively: to a degree exceeding normal or proper limits

Other synonyms of to a fault include overly, too.

to a fault (adverb)	excessively (adverb)
to a degree exceeding normal or proper limits	to a degree exceeding normal or proper limits