Convene erratically to cover surface (6)
I believe the answer is:
veneer
'surface' is the definition.
(thesaurus)
'convene erratically to cover' is the wordplay.
'to cover' says the answer is hidden in the clue (I've seen 'covered' mean this (the answer is covered up by the clue)).
'VENEER' can be found hidden inside 'convene erratically'.
(Other definitions for veneer that I've seen before include "Superficial shine" , "Thin layer on surface, often of furniture" , "Thin decorative covering of fine wood" , "A thin outer layer" , "Thin layer glued to a surface" .)