Try uplifting sign given by an enormous number (6)
I believe the answer is:
googol
'an enormous number' is the definition.
(number written as 1 with a hundred zeroes)
'try uplifting sign given' is the wordplay.
'try' becomes 'go' (both can mean an attempt).
'uplifting' shows that the letters should be reversed in order.
'sign' becomes 'logo' (logo is a kind of sign).
'given' says to put letters next to each other.
'logo' reversed gives 'ogol'.
'go'+'ogol'='GOOGOL'
'by' acts as a link.
(Other definitions for googol that I've seen before include "very large number" , "10100" , "Ten to the power of 100" , "There's a huge amount!" , "Big number" .)