Yearns to match the size (5)
I believe the answer is:
sighs
'yearns' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for sighs that I've seen before include "Exhales audibly" , "Bridge of - - (Venice)" , "Moans" , "Lamentations" , "Yearns" .)