Humbug attracting endless reverence? That’s a laugh (6)
I believe the answer is:
guffaw
'that's a laugh' is the definition.
(guffaw is a kind of laugh)
'humbug attracting endless reverence?' is the wordplay.
'humbug' becomes 'guff'.
'attracting' is a charade indicator (letters next to each other).
'endless' means to remove the last letter.
'reverence?' becomes 'awe' ('awe' can be a synonym of 'reverence').
'awe' with its final letter taken off is 'aw'.
'guff'+'aw'='GUFFAW'
(Other definitions for guffaw that I've seen before include "way of expressing amusement" , "A loud raucous laugh" , "A loud hearty laugh" , "Laugh boisterously" , "Burst of loud, hearty laughter" .)