Basil, perhaps, in another book (4)
I believe the answer is:
herb
'basil' is the definition.
(basil is an example)
'in another book' is the wordplay.
'in' indicates the answer is hidden within the clue.
'HERB' is hidden within 'another book'.
'perhaps' acts as a link.
(Other definitions for herb that I've seen before include "Basil, for example, is one" , "Wayside plant with small red flowers" , "Parsley, sage, rosemary or thyme?" , "Rosemary, for example" , "Simple" .)