Spread support with semiprecious stone (9)
I believe the answer is:
propagate
'spread' is the definition.
(synonyms)
'support with semiprecious stone' is the wordplay.
'support' becomes 'prop' (prop up can mean to support).
'with' means one lot of letters go next to another.
'semiprecious stone' becomes 'agate' (I've seen this in another clue).
'prop'+'agate'='PROPAGATE'
(Other definitions for propagate that I've seen before include "Grow (plants) or spread (ideas)" , "Produce more" , "Promote (an idea) widely" , "Advertise widely" , "Publicise" .)