One has a feeling it may be dropped (5)
I believe the answer is:
aitch
'it may be dropped' is the definition.
The definition suggests a singular noun which matches the answer.
'one has a feeling' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'has' means one lot of letters go next to another.
'a feeling' becomes 'itch' (itch is a kind of feeling).
'a'+'itch'='AITCH'
Can you help me to learn more?
(Other definitions for aitch that I've seen before include "first bit of hymn?" , "The letter h in full" , "Eighth letter of the English alphabet" , "Aspirated letter" , "that I will immediately succeed" .)