untenable vs indefensible

untenable and indefensible both are adjectives.

Word	Noun	Adjective	Verb	Adverb
untenable	No	Yes	No	No
indefensible	No	Yes	No	No

As adjectives, untenable and indefensible are synonyms defined as:

untenable and indefensible: (of theories etc) incapable of being defended or justified

untenable (adjective)	indefensible (adjective)
(of theories etc) incapable of being defended or justified	incapable of being justified or explained
	(of theories etc) incapable of being defended or justified
	not able to be protected against attack