So hard to be among trade union strikers to begin with (4)
I believe the answer is:
thus
'so' is the definition.
(I know that so can be written as thus)
'hard to be among trade union strikers to begin with' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to be among' is an insertion indicator.
'trade union' becomes 'TU' (abbreviation for trade union).
'to begin with' suggests taking the first letters.
The initial letter of 'strikers' is 's'.
'h' inserted inside 'tu' is 'thu'.
'thu'+'s'='THUS'
(Other definitions for thus that I've seen before include "as indicated" , "Like so" , "'So, therefore (4)'" , "As a result" , "Consequently" .)