Tireless gulper, half-cut sibling with wine (10)
I believe the answer is:
persistent
'tireless' is the definition.
(thesaurus)
'gulper half-cut sibling with wine' is the wordplay.
'half cut' indicates taking half.
'sibling' becomes 'sis' (short for sister).
'with' means one lot of letters go next to another.
'wine' becomes 'tent' (type of Spanish wine).
'gulper' cut in half is 'per'.
'per'+'sis'+'tent'='PERSISTENT'
(Other definitions for persistent that I've seen before include "Determined" , "single-minded" , "Dogged" , "Not taking "no" for an answer" , "Endless" .)