Where you might find a US MD getting increasingly silly (6)
I believe the answer is:
inaner
I believe this clue is a double definition.
'where you might find a us md' is the first definition.
(in an ER, emergency room)
'increasingly silly' is the second definition.
(inane can mean silly)
'getting' acts as a link.
(Other definitions for inaner that I've seen before include "Rather silly" , "More stupid" , "More empty" , "More vacuous" , "What's relatively lemon-like" .)