Alarming to be treated as almost irrelevant (8)
I believe the answer is:
marginal
'almost irrelevant' is the definition.
I can't tell whether this defines the answer.
'alarming to be treated' is the wordplay.
'to be treated' indicates an anagram.
'alarming' is an anagram of 'MARGINAL'.
'as' is the link.
Can you help me to learn more?
(Other definitions for marginal that I've seen before include "Borderline" , "On the edges of" , "on border" , "Very slight in amount, at the edge" , "On the fringes" .)