The most common and most likely answer to this crossword clue is the 8 letter word FLOUNDER
I've seen this crossword clue in The Times
F
L
O
U
N
D
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R
More clues leading to the result FLOUNDER
- Fish left in sink
- Sink full of large fish
- Be unsuccessful gripping line for flatfish
- Fish struggle to swim?
- Get into difficulties and go down outside loch
- Fish struggle to stay afloat
- Lake creator’s imported fish
- Struggle helplessly needing father to cross lake
- . Flat dwellers in the main struggle
- Fish get into difficulties
Buddy explains!

The straight part
We know that "fish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fish = flounder.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 FLOUNDER mean?
FLOUNDER noun- A European species of flatfish having dull brown colouring with reddish-brown blotches; fluke, European flounder, Platichthys flesus.
- Any of various flatfish of the family Pleuronectidae or Bothidae.
- A bootmaker's tool for crimping boot fronts.
- To flop around as a fish out of water.
- To make clumsy attempts to move or regain one's balance.
- To act clumsily or confused; to struggle or be flustered.
- To be in serious difficulty.