Endless hope provided by fashionable pain reliever (7)
I believe the answer is:
aspirin
'fashionable pain reliever' is the definition.
I know that 'pain' relates to this answer. I also know that both the answer and definition are singular nouns
'endless hope provided' is the wordplay.
'endless' means to remove the last letter.
'hope' becomes 'aspire' (I've seen this before).
'provided' becomes 'in' (I can't explain this - if you can you should give a lot more credence to this answer).
'aspire' with its final letter taken away is 'aspir'.
'aspir'+'in'='ASPIRIN'
'by' acts as a link.
Can you help me to learn more?
(Other definitions for aspirin that I've seen before include "Commonly used pain-killer" , "number" , "Mild pain-killing drug" , "Common painkiller" , "Sip rain (anag.)" .)