Pub meal main oddly lacking taste (5)
I believe the answer is:
umami
'taste' is the definition.
(I've seen this before)
'pub meal main oddly lacking' is the wordplay.
'oddly lacking' indicates alternate letters.
'pub'+'meal'+'main'='pubmealmain'
The alternate letters of 'pubmealmain' are 'UMAMI'.
(Other definitions for umami that I've seen before include "acquired taste perhaps" , "Savoury taste sensation produced by glutamates - I, a mum (anag)" , "Fifth flavour" , "Japanese word for pleasant savoury taste" , "meaty taste" .)