The aside is transformed by original thoughts (5)
I believe the answer is:
ideas
'original thoughts' is the definition.
'ideas' can be an answer for 'thoughts' ('idea' can be a synonym of 'thought'). I am unsure of the 'original' bit.
'the aside is transformed' is the wordplay.
'is transformed' indicates an anagram.
'aside' is an anagram of 'IDEAS'.
'by' is the link.
Can you help me to learn more?
(Other definitions for ideas that I've seen before include "Fancies" , "Thoughts, creative perhaps" , "Thoughts, concepts" , "Thoughts, maybe creative" , "thinking" .)