Side of letter I forgot to write (5)
I believe the answer is:
chips
'i forgot to write' is the definition.
I can't judge whether this definition defines the answer.
'side of letter' is the wordplay.
I cannot really understand how this works, but
'letter' could be 'chi' (Greek letter) and 'chi' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for chips that I've seen before include "Gambling counters" , "French fries" , "Flakes" , "Betting tokens" , "accompaniment to 24 [FISH DISH]" .)