The most common and most likely answer to this crossword clue is the 8 plus 10 letter word IRONSIDE (DERISION)
I
R
O
N
S
I
D
E
(
D
E
R
I
S
I
O
N
)
Buddy explains!
The straight part
We know that "Puritan" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case puritan = ironside (derision).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.