The most common and most likely answer to this crossword clue is the 4 letter word PERK
I've seen this crossword clue in Independent
P
E
R
K
Buddy explains!
The straight part
We know that "Bonus" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bonus = perk.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 PERK mean?
PERK noun- Perquisite.
- A bonus ability that a player character can acquire; a permanent power-up.
- A percolator, particularly of coffee.
- To make (coffee) in a percolator or a drip coffeemaker.
- Of coffee: to be produced by heated water seeping (“percolating”) through coffee grounds.
- To make trim or smart; to straighten up; to erect; to make a jaunty or saucy display of.
- To appear from below or behind something, emerge, pop up, poke out.
- To exalt oneself; to bear oneself loftily.
- Smart; trim; spruce; jaunty; vain.
- To peer; to look inquisitively.
- To perch.