Maiden buried in textbook is more stuffy (7)

'more stuffy' is the definition.
(prim can mean stuffy or proper)

'maiden buried in textbook' is the wordplay.
'maiden' becomes 'm' (cricket abbreviation).
'buried in' indicates putting letters inside (inserted letters get buried).
'textbook' becomes 'primer' (primer is a kind of textbook).
'm' put within 'primer' is 'PRIMMER'.

'is' is the link.