The most common and most likely answer to this crossword clue is the 10 letter word REASONABLE
I've seen this crossword clue in The Sunday Telegraph
R
E
A
S
O
N
A
B
L
E
More clues leading to the result REASONABLE
- Referring to a relative, competent, fair
- Aim to get fit, being wise
- Work out to get fit — that’s making sense
- Fair where dancing bear on sale
- Subversive gets beheaded? That’s OK
- Goal accomplished? Just
- About A Boy: accomplished, wise
- Just a ban, or else reforms
- Showing disloyalty, dismissing head? That’s okay
- Inexpensive woolly bear on sale
Buddy explains!

The straight part
We know that "okay" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case okay = reasonable.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 REASONABLE mean?
REASONABLE adjective- Having the faculty of reason; rational, reasoning.
- Just; fair; agreeable to reason.
- Not excessive or immoderate; within due limits; proper.
- Not expensive; fairly priced.
- Satisfactory.