The European man-of-war may have a deadly sting (10)
I believe the answer is:
portuguese
'the european man-of-war' is the definition.
'Portuguese' can be an answer for 'man-of-war' (synonyms). I'm not sure about the 'the european' bit.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for portuguese that I've seen before include "description of a man-of-war?" , "Language of Brazil" , "Like da Gama" , "EU national" , "Eg, Native to Lisbon" .)