What may creep in via yard at first (3)
I believe the answer is:
ivy
'what may creep' is the definition.
I can't judge whether this definition defines the answer.
'in via yard at first' is the wordplay.
'at first' says to take the initial letters.
The initial letters of 'in via yard' is 'IVY'.
Can you help me to learn more?
(Other definitions for ivy that I've seen before include "Female" , "Poisonous plant" , "The Hedera genus of evergreen climbers" , "Girl's name; climber" , "Climbing-plant" .)