North America's largest alpine lake (5)
I believe the answer is:
tahoe
'north america's largest alpine lake' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tahoe that I've seen before include "Mountain lake" , "Lake/desert resort on the California-Nevada border" , "Nevada/California lake" , "US lake" , "Lake in Sierra Nevada mountains" .)