Penny's absorbing book: 'Seasons' (9)
I believe the answer is:
preserves
'seasons' is the definition.
The answer and definition can be both related to change as well as being verbs in their -s form.
Perhaps they are linked in a way I don't understand?
'penny's absorbing book' is the wordplay.
'penny's' becomes 'ps'.
'absorbing' means one lot of letters goes inside another.
'book' becomes 'reserve' ('reserve' can be a synonym of 'book'**).
'ps' going around 'reserve' is 'PRESERVES'.
Can you help me to learn more?
(Other definitions for preserves that I've seen before include "Keeps in unchanged condition, or from decay" , "Keeps in unaltered condition" , "Keeps the jams" , "Items sold at school fetes" , "Stores - pickles" .)