Some quakers (6)
I believe the answer is:
aspens
'some quakers' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for aspens that I've seen before include "Trembling poplars" , "Trees that shiver, kind of poplars" , "Quivering poplars" , "Kind of poplars with shivering leaves" , "Trees with leaves that quiver" .)