Old couple boarding vessel exhausted (7)
I believe the answer is:
outworn
'exhausted' is the definition.
(I've seen this before)
'old couple boarding vessel' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'couple' becomes 'two' (a couple can mean two of something).
'boarding' means one lot of letters goes inside another.
'vessel' becomes 'urn' (urn is a type of container).
'two' going inside 'urn' is 'utworn'.
'o'+'utworn'='OUTWORN'
(Other definitions for outworn that I've seen before include "Old-fashioned" , "Jaded" , "Old, exhausted or no longer used as dress" , "Out of date" , "Obsolete, dated" .)