thump vs thud

thump and thud both are nouns.

Word	Noun	Adjective	Verb	Adverb
thump	Yes	No	Yes	No
thud	Yes	No	Yes	No

As nouns, thump and thud are synonyms defined as:

Other synonyms of thump include clump, clunk, thumping.

As verbs, thump and thud are synonyms defined as:

thump (noun)	thud (noun)
a heavy blow with the hand	a heavy dull sound (as made by impact of heavy objects)
a heavy dull sound (as made by impact of heavy objects)

thump (verb)	thud (verb)
hit hard with the hand, fist, or some heavy instrument	strike with a dull sound
move rhythmically	make a dull sound
make a dull sound	make a noise typical of an engine lacking lubricants