Warnings from nearly all branches (6)
I believe the answer is:
alarms
'warnings' is the definition.
(I've seen this before)
'nearly all branches' is the wordplay.
'nearly all' becomes 'al'.
'branches' becomes 'arms' ('arm' can be a synonym of 'branch').
'al'+'arms'='ALARMS'
'from' acts as a link.
(Other definitions for alarms that I've seen before include "Warning clocks that wake us up" , "Warning sounds" , "Danger signals" , "Scares or startles" , "Frightens, scares" .)