He will shortly ring - to say this? (5)
I believe the answer is:
hello
'ring to say this?' is the definition.
The definition suggests a singular noun which matches the answer.
'he will shortly' is the wordplay.
'will' becomes ''ll' (contracted form, as in 'he'll' - 'he will').
'shortly' becomes 'o' (I can't explain this - if you can you should give a lot more credence to this answer).
'he'+'ll'+'o'='HELLO'
Can you help me to learn more?
(Other definitions for hello that I've seen before include "Conversation starter" , "Welcome" , "royals dominate its pages?" , "opener?" , "Surprised cry" .)