The most common and most likely answer to this crossword clue is the 10 letter word BY-PRODUCT
I've seen this crossword clue in Financial Times
B
Y
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P
R
O
D
U
C
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More clues leading to the result BY-PRODUCT
Buddy explains!
The straight part
We know that "Bit on the side" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bit on the side = by-product.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 BY-PRODUCT mean?
BY-PRODUCT noun- A secondary product; something made incidentally during the production of something else.
- A side effect.