Medicament required when one has duck to eat? (6)
'medicament' is the definition.
(iodine is a kind of medicament)
'when one has duck to eat?' is the wordplay.
'when one' becomes 'i' (Roman numeral. I am not sure about the 'when' bit.).
'has' says to put letters next to each other.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'to eat?' becomes 'dine' (dining is a kind of eating).
'required' acts as a link.
Can you help me to learn more?
(Other definitions for iodine that I've seen before include "Element forming black crystals or violet vapour", "Disinfectant made from seaweed", "Element, atomic number 53", "Black crystalline element", "Element that can exist as a purple vapour".)