Brainchild of Theban king protecting a palmlike plant (8)
I believe the answer is:
creation
'brainchild' is the definition.
(thesaurus)
'theban king protecting a palmlike plant' is the wordplay.
'theban king' becomes 'creon' (figure of Greek myth).
'protecting' indicates putting letters inside (inserted letters are held or protected).
'palmlike plant' becomes 'ti' (ti is a type of flowering plant).
'a'+'ti'='ati'
'creon' placed around 'ati' is 'CREATION'.
'of' is the link.
(Other definitions for creation that I've seen before include "A thing made or invented" , "Haydn oratorio" , "concept" , "Something that has been made" , "New product" .)