Grass and cannabis elevated many pipes (4,4)
I believe the answer is:
reed stop
'many pipes' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'grass and cannabis elevated' is the wordplay.
'grass' becomes 'reed' (type of grass plant).
'and' means one lot of letters go next to another.
'cannabis' becomes 'pots' (I am not sure about this - if you are sure you should believe this answer much more).
'elevated' says the letters should be written backwards (in a down clue, letters go up).
'pots' reversed gives 'stop'.
'reed'+'stop'='REED-STOP'
Can you help me to learn more?
(Other definitions for reed stop that I've seen before include "Set of organ pipes; do preset (anag.)" , "part of organ" .)