What appears regularly in diary? (3)
I believe the answer is:
day
'what appears' is the definition.
I can't judge whether this definition defines the answer.
'regularly in diary?' is the wordplay.
'regularly in' means one should take alternating letters.
The alternate letters of 'diary' are 'DAY'.
Can you help me to learn more?
(Other definitions for day that I've seen before include "Dawn to dusk" , "Lewis as poet" , "24-hour period" , "24 23 acrosses" , "Twenty-four hours" .)