One of the M's in MoMA (6)
I believe the answer is:
modern
'one of the m's in moma' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for modern that I've seen before include "Of the present time or current fashion" , "Belonging to the present time" , "The very latest available" , "'Contemporary, up-to-the-minute (6)'" , "Activity of 18 ac" .)