The most common and most likely answer to this crossword clue is the 4 letter word GROW
I've seen this crossword clue in The Times
G
R
O
W
Buddy explains!

The straight part
We know that "Develop" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case develop = grow.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 GROW mean?
GROW verb- To become larger, to increase in magnitude.
- To appear or sprout.
- To develop, to mature.
- To cause or allow something to become bigger, especially to cultivate plants.
- To assume a condition or quality over time.
- To become attached or fixed; to adhere.