Aspiring welder's first double shifts (5-2)
I believe the answer is:
would-be
'aspiring' is the definition.
('would-be' can be a synonym of 'aspiring')
'welder's first double shifts' is the wordplay.
'first' indicates taking the first letters.
'shifts' is an anagram indicator.
The first letter of 'welder' is 'w'.
'double' with letters rearranged gives 'ouldbe'.
'w'+'ouldbe'='WOULD-BE'
(Other definitions for would-be that I've seen before include "Pretender" , "One aspiring to what they are not" , "Blew duo away for desiring or pretending" , "See 13" .)