Bizarrely, learnt rapture is extraordinary (13)
I believe the answer is:
preternatural
'extraordinary' is the definition.
(similar in meaning)
'bizarrely learnt rapture' is the wordplay.
'bizarrely' indicates anagramming the letters.
'learnt'+'rapture'='learntrapture'
'learntrapture' anagrammed gives 'PRETERNATURAL'.
'is' acts as a link.
(Other definitions for preternatural that I've seen before include "Abnormal" , "Weird - extraordinary" , "beyond what's normal" , "Very unusual" .)