One hoping for a lift from big song, say, by pop singer (7)
I believe the answer is:
hitcher
'one hoping for a lift' is the definition.
The definition suggests a singular noun which matches the answer.
'big song say by pop singer' is the wordplay.
'big song say' becomes 'hit' (I can't explain this - if you can you should give a lot more credence to this answer).
'by' means one lot of letters go next to another.
'pop singer' becomes 'Cher' (Cher is an American singer).
'hit'+'cher'='HITCHER'
'from' is the link.
Can you help me to learn more?
(Other definitions for hitcher that I've seen before include "traveller" , "I count on thumb" , "one determined to get somewhere" .)