Head stableboy drove off with a lively horse (5)

I believe the answer is:

steed

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

'lively horse' is the definition.
(I've seen this in another clue)

I don't understand the rest of the clue.

(Other definitions for steed that I've seen before include "Trusty horse" , "Spirited horse" , "Stallion" , "(Poetic) horse" , "ride" .)

I've seen this clue in The Globe and Mail.

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