The most common and most likely answer to this crossword clue is the 9 letter word CROCODILE
I've seen this crossword clue in The Guardian
C
R
O
C
O
D
I
L
E
More clues leading to the result CROCODILE
- Old Cicero’s untidy file
- Source of unreal grief — water hazard?
- Cold part in which fish is taken by one reptile
- Reptile, ice-cold or otherwise?
- Line of children seeing potential danger in water
- One’s snappy seeing cool cider being drunk
- Group of pupils on walk to find powerful animal
- Proverbially, it cried cool tears
- Ice-cold or otherwise, one’s emotion is considered insincere
- Recoil, struggling to eat fish – a snapper?
Buddy explains!

The straight part
We know that "file" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case file = crocodile.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 CROCODILE mean?
CROCODILE noun- Any of the predatory amphibious reptiles of the family Crocodylidae; a crocodilian, any species of the order Crocodilia, which also includes the alligators, caimans and gavials.
- A long line or procession of people (especially children) walking together.
- A fallacious dilemma, mythically supposed to have been first used by a crocodile.
- To speak one's native language at an Esperanto-language gathering, rather than Esperanto.