Maybe hot lemon, nothing less, can help when you've a cold (7)
I believe the answer is:
menthol
'help when you've a cold' is the definition.
I can't judge whether this definition defines the answer.
'maybe hot lemon nothing less' is the wordplay.
'maybe' indicates an anagram.
'nothing' becomes 'O' (looks like zero - 0).
'less' suggests deleting specific letters (less can mean minus).
'hot'+'lemon'='hotlemon'
'hotlemon' with 'o' removed is 'htlemon'.
'htlemon' with letters rearranged gives 'MENTHOL'.
'can' is the link.
Can you help me to learn more?
(Other definitions for menthol that I've seen before include "Soothing substance from peppermint" , "Camphor used as a decongestant" , "Peppermint camphor" , "Substance from peppermint oil used as flavouring." , "mild analgesic" .)