One giving a talk - on the radio? (7)
I believe the answer is:
speaker
'one giving a talk on the radio?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'one giving a talk on the radio?' is the wordplay.
'one giving' means one lot of letters go next to another.
'a talk' becomes 'speak' (I've seen this before).
'on the radio?' becomes 'er' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'speak' put next to 'er' is 'SPEAKER'.
Can you help me to learn more?
(Other definitions for speaker that I've seen before include "Person presiding over British House of Commons or similar assembly" , "audio equipment" , "Parliamentary authority" , "Orator" , "Presiding officer of the US House of Represtatives" .)