Satanic sort enters, wickedly seizing power (7)
I believe the answer is:
serpent
'satanic sort' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'enters wickedly seizing power' is the wordplay.
'wickedly' indicates anagramming the letters.
'seizing' is an insertion indicator.
'power' becomes 'p' (symbol in physics).
'enters' anagrammed gives 'serent'.
'serent' going around 'p' is 'SERPENT'.
Can you help me to learn more?
(Other definitions for serpent that I've seen before include "Early wind instrument" , "Instrument of the past" , "Venomous snake" , "the first lady found beguiling" , "Tempting" .)