Antonym of UNTENABLE:

• Untenable (adjective):
English Meaning:
1. not capable of being defended against attack or criticism; not tenable.
2. not able to be supported or defended against criticism, or no longer able to continue.
Bangla Meaning: অসমর্থনীয়; অচল; অসমর্থনযোগ্য; খাটে না এমন; অধার্য; অগ্রাহ্য; অসমর্থনীয়; অগ্রহণীয়।

• Synonyms: unreasonable, invalid, misled, absurd, inconsistent, unfounded, unsupported, illogical.

• Antonyms: confirmed, rational, certified, true, sensible, real, wise, actual, validated, certain.

Example of Sentences:
- Unfortunately, that theory has been untenable for more than fifty years.
- We argue here that these discontinuities are untenable.
- The position of the players’ union has become untenable.

Source:
1. Accessible Dictionary.
2. Cambridge Dictionary.
3. Merriam-webster Dictionary.