Beat El Cid Eddy? Thoroughly! (9)

I believe the answer is:

decidedly

I'm a little stuck... Click here to teach me more about this clue!

'thoroughly' is the definition.
Both the answer and definition are adverbs. Perhaps there's an association between them I don't understand?

'beat el cid eddy?' is the wordplay.
'beat' indicates anagramming the letters.
'el'+'cid'+'eddy'='elcideddy'
'elcideddy' with letters rearranged gives 'DECIDEDLY'.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app