Spot book on language with preface missing (7)
I believe the answer is:
blemish
'spot' is the definition.
(I know that spot can be written as blemish)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for blemish that I've seen before include "Stain, flaw" , "A flaw or imperfection" , "deformity" , "bad mark?" , "Flaw that spoils a thing's perfection" .)