The most common and most likely answer to this crossword clue is the 5 letter word CHOSE
I've seen this crossword clue in Financial Times
C
H
O
S
E
Buddy explains!

The straight part
We know that "Decided on" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case decided on = chose.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 CHOSE mean?
CHOSE verb- To pick; to make the choice of; to select.
- To elect.
- To decide to act in a certain way.
- To wish; to desire; to prefer.
- A thing; personal property.