Detect hint of marjoram in stock (5)
I believe the answer is:
smell
'detect' is the definition.
(I've seen this in another clue)
'hint of marjoram in stock' is the wordplay.
'hint of' says to take the initial letters (the smallest possible amount of the word).
'in' is an insertion indicator.
'stock' becomes 'sell'.
The first letter of 'marjoram' is 'm'.
'm' going within 'sell' is 'SMELL'.
(Other definitions for smell that I've seen before include "Nasal sense" , "Sniff" , "Scent" , "Unpleasant odour" , "Perceive through the nose" .)