I have followed the crowd - it's tremendous (7)
I believe the answer is:
massive
'tremendous' is the definition.
(thesaurus)
'i have followed the crowd' is the wordplay.
'i have' becomes 'I've' (contraction of 'I have').
'followed' says to put letters next to each other.
'the crowd' becomes 'mass' (I've seen this before).
'ive' put after 'mass' is 'MASSIVE'.
'it's' acts as a link.
(Other definitions for massive that I've seen before include "Gargantuan" , "Enormous" , "Colossal" , "Exceptionally large" , "Large, solid" .)