Grade one. started smoking some weed (5)
I believe the answer is:
grass
'weed' is the definition.
(I know that weed can be written as grass)
'grade one started smoking some' is the wordplay.
'grade' becomes 'grad' (synonyms).
'one started' means to remove the last letter (I've seen 'starts' mean this).
'smoking some' becomes 'ss' (this could be a standard abbreviation which I don't know about).
'grad' with its final letter removed is 'gra'.
'gra'+'ss'='GRASS'
Can you help me to learn more?
(Other definitions for grass that I've seen before include "blades" , "Pasturage" , "Ruminants' food" , "Give away" , "What meadowlark perches on" .)