Appointment book of Irish God rarely empty (5)
I believe the answer is:
diary
'appointment book' is the definition.
(I've seen this before)
'irish god rarely empty' is the wordplay.
'irish god' becomes 'dia' (I am not sure about this - if you are sure you should believe this answer much more).
'empty' says to hollow out the word (remove centre letters).
'rarely' with its middle removed is 'ry'.
'dia'+'ry'='DIARY'
'of' is the link.
Can you help me to learn more?
(Other definitions for diary that I've seen before include "Log of daily activity" , "Personal journal" , "Daily record of personal activity" , "Appointment book" , "Pepys's record" .)