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 defines the answer.
'side of letter' is the wordplay.
I cannot quite see how this works, but
'letter' could be 'chi' (Greek letter) and 'chi' is found in the answer.
This explanation may well be incorrect...
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]" .)