The old song urges to let a smile be yours (8)
I believe the answer is:
umbrella
'the old song urges to let a smile be yours' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for umbrella that I've seen before include "Collapsible ribbed canopy against rain" , "Parasol" , "What may go up when the rain comes down" , "The old song urges to let a smile be yours" , "requirement in poor weather" .)