Some green or seasick Viking (5)
I believe the answer is:
norse
'viking' is the definition.
(the Vikings were a Norse people)
'some green or seasick' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'NORSE' is hidden in the letters of 'green or seasick'.
(Other definitions for norse that I've seen before include "Old Scandinavian language" , "Northern European" , "like the Valkyries?" , "Relating to ancient Scandinavian" , "Old Scandinavian tongue" .)