Handy reference book (6)
I believe the answer is:
manual
I believe this is a triple definition!
'handy' is the first definition.
(I've seen this before)
'reference' is the second definition.
(manual is a kind of reference)
'book' is the third definition.
(manual is a kind of book)
(Other definitions for manual that I've seen before include "Working with the hands" , "Done by hand, or a handbook" , "Instruction book prepared by hand?" , "Handy" , "Operated by hand" .)