Cryptic crossword clue
Unsurpassed wit — foster-father cracks up 2,3,5,5

The most common and most likely answer to this crossword clue is the 2 plus 3 plus 5 plus 5 letter word OF THE FIRST WATER

I've seen this crossword clue in The Daily Telegraph
O
F
T
H
E
F
I
R
S
T
W
A
T
E
R

Buddy explains!

The straight part
We know that "Unsurpassed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unsurpassed = of the first water.
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.

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