What does the cryptic crossword clue "Giant in dispute with neighbour idly playing with alien (9)" mean?

The wordplay uses an anagram. anagram of IDLY (synonym="IDLY") + ALIEN (synonym="ALIEN") = LEYLANDII The answer is LEYLANDII.

Giant in dispute with neighbour idly playing with alien (9)

Guardian Cryptic #26511 | 16 Down | 2015-03-05 flower