Nothing in the growth trend right for person who speculates (9)
I believe the answer is:
theoriser
'trend right for person who speculates' is the definition.
The definition suggests a singular noun which matches the answer.
'nothing in the growth' is the wordplay.
'nothing' becomes 'O' (O resembles 0).
'in' means one lot of letters goes inside another.
'growth' becomes 'riser' (I can't explain this - if you can you should believe this answer much more).
'the'+'riser'='theriser'
'o' inserted within 'theriser' is 'THEORISER'.
Can you help me to learn more?
(Other definitions for theoriser that I've seen before include "one who speculates" , "One who reasons" , "he thinks" , "speculator" , "One who has convictions" .)