Novice recruited by noble legion (9)
I believe the answer is:
countless
'legion' is the definition.
(I've seen this before)
'novice recruited by noble' is the wordplay.
'novice' becomes 'L' (as in a learner driver with L-plates on their car).
'recruited by' is an insertion indicator.
'noble' becomes 'countess' (I've seen this before).
'l' put inside 'countess' is 'COUNTLESS'.
(Other definitions for countless that I've seen before include "not so important" , "Legion seeming to be" , "Untold" , "Innumerable" , "Very many" .)