Small women's group on ship is foreign (5)
I believe the answer is:
swiss
'foreign' is the definition.
'small women's group on ship' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'women's group' becomes 'wi' (Women's Institute).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
's'+'wi'+'ss'='SWISS'
'is' is the link.
(Other definitions for swiss that I've seen before include "Native to Geneva, say" , "Word linking cheese and roll" , "-- Cheese plant; -- roll" , "Native to Berne" , "Helvetian" .)