extended vs lengthy

extended and lengthy both are adjectives.

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

As adjectives, extended and lengthy are synonyms defined as:

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

extended (adjective)	lengthy (adjective)
fully extended or stretched forth	relatively long in duration; tediously protracted
beyond the literal or primary sense
large in spatial extent or range or scope or quantity
drawn out or made longer spatially
relatively long in duration; tediously protracted