Second man on the Moon (6)
I believe the answer is:
aldrin
'second man on the moon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for aldrin that I've seen before include "'Buzz' -, US astronaut" , "Buzz, second man on moon" , "Buzz . . . . . ., moonwalker" .)