Druid regularly seen as useless (3)
I believe the answer is:
dud
'useless' is the definition.
(I've seen this before)
'druid regularly seen' is the wordplay.
'regularly seen' indicates alternate letters.
The alternating letters of 'druid' are 'DUD'.
'as' is the link.
(Other definitions for dud that I've seen before include "Broken" , "One failing to work, explode" , "Useless, doesn't work - a palindrome" , "Failed, worthless thing" , "Firework not going up" .)