What you’ll see in a diary, regularly ending in darkness (4)
I believe the answer is:
days
'what you'll see' is the definition.
I can't tell whether this defines the answer.
'a diary regularly ending in darkness' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'ending in' suggests the final letters.
The final letter of 'darkness' is 's'.
The alternating letters of 'diary' are 'day'.
'day'+'s'='DAYS'
'in' is the link.
Can you help me to learn more?
(Other definitions for days that I've seen before include "Units of time" , "Sevenths of a week" , "Time period(s)" , "Periods of 24 hours" , "See 7 and 18" .)