Remarkable help one man arranged (10)
I believe the answer is:
phenomenal
'remarkable' is the definition.
(I've seen this before)
'help one man arranged' is the wordplay.
'arranged' indicates an anagram.
'help'+'one'+'man'='helponeman'
'helponeman' with letters rearranged gives 'PHENOMENAL'.
(Other definitions for phenomenal that I've seen before include "Extraordinary - help one man (anag)" , "Incredible" , "Exceptionally good" , "Stunning" , "Remarkable" .)