The most common and most likely answer to this crossword clue is the 3 plus 5 letter word ONE LINER
I've seen this crossword clue in The Daily Telegraph
O
N
E
L
I
N
E
R
More clues leading to the result ONE LINER
Buddy explains!

The straight part
We know that "Joke" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case joke = one liner.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 ONE LINER mean?
ONE LINER noun- A short joke, especially one of a single sentence.
- A short remark intended as a sound bite.
- A command or small program consisting of a single line of input.