Restaurant is more drab without soldier (5)
I believe the answer is:
diner
'restaurant' is the definition.
(diner is a kind of restaurant)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for diner that I've seen before include "Restaurant customer" , "American restaurant" , "(One using) restaurant car" , "one at banquet?" , "One taking a meal" .)