Marginal difference is enough to make one afraid (8)
I believe the answer is:
alarming
'enough to make one afraid' is the definition.
I can't tell whether this defines the answer.
'marginal difference' is the wordplay.
'difference' indicates anagramming the letters.
'marginal' is an anagram of 'ALARMING'.
'is' is the link.
Can you help me to learn more?
(Other definitions for alarming that I've seen before include "Striking with fear" , "Dreadful" , "Frightening or warning of danger" , "Disturbing, frightening" , "causing fright" .)