The most common and most likely answer to this crossword clue is the 7 letter word TENABLE
I've seen this crossword clue in The Guardian
T
E
N
A
B
L
E
More clues leading to the result TENABLE
- Defensible points accepted by board
- Credible number left in Lincoln
- A number competent? That’s credible
- Seemingly rational little gap in record
- Number clever enough for game show
- Credible chart about space
- Only one of the eleven incompetent? That can be defended
- Number with clever sound
- Credible catch, stored in box
- Lowest honour having enough power that can be retained
Buddy explains!

The straight part
We know that "Credible" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case credible = tenable.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TENABLE mean?
TENABLE adjective- (of a theory, argument, etc.) capable of being maintained or justified; well-founded
- Capable of being defended against assault or attack; defensible
- Fit for habitation, similar, or related use.