The most common and most likely answer to this crossword clue is the 13 letter word LEXICOGRAPHER
L
E
X
I
C
O
G
R
A
P
H
E
R
More clues leading to the result LEXICOGRAPHER
Buddy explains!

The straight part
We know that "Partridge, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case partridge, say = lexicographer.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 LEXICOGRAPHER mean?
LEXICOGRAPHER noun- One who writes or compiles a dictionary