Nowadays has foundation belittled (6)
I believe the answer is:
abased
'belittled' is the definition.
(I've seen this in another clue)
'nowadays has foundation' is the wordplay.
'nowadays' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
'has' indicates putting letters inside.
'foundation' becomes 'base' (synonyms).
'ad' going around 'base' is 'ABASED'.
(Other definitions for abased that I've seen before include "Demeaned (oneself)" , "Degraded, brought low" , "Belittled, degraded" , "Degraded, humbled" , "Humbled, mortified" .)