Modern in only one way (3)
I believe the answer is:
Here is my best explanation:
'modern' is the definition.
('new' is associated in meaning with 'modern')
'in only one way' is the wordplay.
'in' says the answer is hidden in the clue.
'NEW' can be found hidden inside 'only one way'.
(Other definitions for new that I've seen before include "Modern", "Fresh, unused", "Not previously used", "Seen for the first time", "Unfamiliar, restored", "Original", "fresh, novel", "Not existing before", "Fresh, recent" and "Unused or novel".)