With the day almost over, it flies! (4)
I believe the answer is:
dove
'it flies' is the definition.
The definition suggests a singular noun which matches the answer.
'with the day almost over' is the wordplay.
'with' says to put letters next to each other.
'the day' becomes 'd' (abbreviation for day).
'almost' means to remove the last letter (almost the whole word is kept).
'over' with its last letter taken off is 'ove'.
'd' put next to 'ove' is 'DOVE'.
Can you help me to learn more?
(Other definitions for dove that I've seen before include "So-called pacifist" , "Peace lover; bird" , "A peaceful bird?" , "Mourning, collared, bird" , "Bird[s]" .)