Superlative form of brambly; the most covered with brambles or prickly shrubs; extremely thorny and tangled.
From 'bramble' plus the superlative suffix '-iest'. This is the highest degree of comparison for bramble-covered places.
The 'brambliest' parts of English hedgerows are also the safest places for birds to nest—predators can't reach them without getting torn up by thorns!
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