Benedict Arnold's lake (4)
I believe the answer is:
tarn
'lake' is the definition.
(tarn is a kind of lake)
'benedict arnold's' is the wordplay.
'TARN' is hidden in amongst the letters.
However, I'm not sure how the hidden word is indicated.
Can you help me to learn more?
(Other definitions for tarn that I've seen before include "Small mountain lake" , "High water" , "Mountain pool: French department" , "Scottish mountain lake" .)