Doctor seals test? That's improper (9)
I believe the answer is:
tasteless
'improper' is the definition.
(I've seen this before)
'doctor seals test?' is the wordplay.
'doctor' indicates an anagram.
'seals'+'test'='sealstest'
'sealstest' anagrammed gives 'TASTELESS'.
'that's' is the link.
(Other definitions for tasteless that I've seen before include "Insipid - vulgar" , "Bland; offensive" , "Lacking flavour or ability to appreciate the beautiful" , "Insipid - inappropriate - dull" , "Unseemly" .)