Ample librarian trained as a dancer (5,9)
I believe the answer is:
prima ballerina
'a dancer' is the definition.
(prima ballerina is a kind of dancer)
'ample librarian trained' is the wordplay.
'trained' indicates anagramming the letters (train can mean to shape or manipulate).
'ample'+'librarian'='amplelibrarian'
'amplelibrarian' is an anagram of 'PRIMA BALLERINA'.
'as' is the link.
(Other definitions for prima ballerina that I've seen before include "Chief female dancer" , "athletic star" .)