Introduction to book by mere poet (5)
I believe the answer is:
blake
'poet' is the definition.
(William Blake)
'introduction to book by mere' is the wordplay.
'introduction to' indicates taking the first letters.
'by' means one lot of letters go next to another.
'mere' becomes 'lake' (I've seen this before).
The initial letter of 'book' is 'b'.
'b'+'lake'='BLAKE'
(Other definitions for blake that I've seen before include "Songs of Innocence poet" , "artistic poet" , "William -, English poet, artist and visionary" , "Exposed (to the air)" , "William --, English poet/visionary" .)