Most rough thickets spread across empty estuaries (10)
I believe the answer is:
sketchiest
'most rough' is the definition.
Both the definition and answer are superlative adjectives. Maybe there's an association between them I don't understand?
'thickets spread across empty estuaries' is the wordplay.
'spread' indicates an anagram.
'across' is an insertion indicator.
'empty' means to remove the middle letters.
'estuaries' with its centre removed is 'es'.
'thickets' anagrammed gives 'sketchit'.
'sketchit' enclosing 'es' is 'SKETCHIEST'.
Can you help me to learn more?
(Another definition for sketchiest that I've seen is " Most snatched".)