Temporary job given to this worker, I see - that's tremendous (8)
I believe the answer is:
gigantic
'that's tremendous' is the definition.
(synonyms)
'temporary job given to this worker i see' is the wordplay.
'temporary job given' becomes 'gig' (I am not sure about this - if you are sure you should believe this answer much more).
'to this worker' becomes 'ant' (worker is a type of ant).
'see' becomes 'C' (the word for the letter, according to Chambers).
'gig'+'ant'+'i'+'c'='GIGANTIC'
Can you help me to learn more?
(Other definitions for gigantic that I've seen before include "Thumping" , "'Enormous, mammoth (8)'" , "Sizeable" , "Exceedingly large" , "Stupendous" .)