Old couple yearn for tea (6)
I believe the answer is:
oolong
'tea' is the definition.
(oolong is a kind of tea)
'old couple yearn' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'couple' shows that letters should be duplicated.
'yearn' becomes 'long' ('long' can be a synonym of 'yearn').
'o' doubled is 'oo'.
'oo'+'long'='OOLONG'
'for' is the link.
(Other definitions for oolong that I've seen before include "Chinese tea leaves - no logo (anag)" , "Kind of Chinese tea" , "Kind of China tea" , "sort of leaves" , "oriental tea" .)