Letters associated with pencil broken by Queen Rosemary, perhaps (4)
I believe the answer is:
herb
'rosemary perhaps' is the definition.
(rosemary is a kind of herb)
'letters associated with pencil broken by queen' is the wordplay.
'letters associated with pencil' becomes 'hb' (HB pencil).
'broken by' indicates putting letters inside.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'hb' going around 'er' is 'HERB'.
(Other definitions for herb that I've seen before include "Bouquet garni component" , "Rosemary perhaps" , "Rosemary, for example" , "Plant with leaves or seeds used medicinally" , "Medicinal or culinary plant" .)