lengthy vs prolonged

lengthy and prolonged both are adjectives.

Word	Noun	Adjective	Verb	Adverb
lengthy	No	Yes	No	No
prolonged	No	Yes	No	No

As adjectives, lengthy and prolonged are synonyms defined as:

lengthy and prolonged: relatively long in duration; tediously protracted

Other synonyms of lengthy include drawn-out, extended, protracted.

lengthy (adjective)	prolonged (adjective)
relatively long in duration; tediously protracted	drawn out or made longer spatially
	relatively long in duration; tediously protracted