Not the first to leave Italian port after Mass for members of The Acer family (6)
I believe the answer is:
maples
'mass for members of the acer family' is the definition.
I can't tell whether this definition defines the answer.
'not the first to leave italian port after' is the wordplay.
'not' becomes 'm' (I am not sure about this - if you are sure you should believe this answer much more).
'the first to leave' means to remove the first letter (the first letter leaves).
'italian port' becomes 'naples' (I've seen this in another clue).
'after' means one lot of letters go next to another.
'naples' with its initial letter removed is 'aples'.
'm'+'aples'='MAPLES'
Can you help me to learn more?
(Other definitions for maples that I've seen before include "Trees of Canada" , "Trees providing syrup" , "MP sale of trees" , "Acers" , "(Canadian) trees" .)