Endless fortune I had put together, that's clear (5)
I believe the answer is:
lucid
'clear' is the definition.
(similar in meaning)
'endless fortune i had put together' is the wordplay.
'endless' means to remove the last letter.
'fortune' becomes 'luck' (synonyms).
'i had' becomes 'i'd' (contraction).
'put together' is a charade indicator (letters next to each other).
'luck' with its last letter removed is 'luc'.
'luc'+'id'='LUCID'
'that's' is the link.
(Other definitions for lucid that I've seen before include "Clear; making sense" , "Clear, easily understandable" , "Clear; bright" , "unlike 5 [OPAQUE]" , "Thinking clearly" .)