The most common and most likely answer to this crossword clue is the 5 letter word ATTAP
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T
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The straight part
We know that "something supplying effective cover" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case something supplying effective cover = attap.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 ATTAP mean?
ATTAP noun- Nipa; a palm tree of the species Nypa fruticans.
- (Southeast Asia) Thatch made from leaves of the nipa palm.