Too many people spell 'phosphorus' in a bad way (9)
I believe the answer is:
overspill
'a bad way' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'too many people spell phosphorus in' is the wordplay.
'too many' becomes 'over' (I've seen this in other clues).
'people spell' becomes 'sill' (I can't explain this - if you can you should believe this answer much more).
'phosphorus' becomes 'P' (P is the chemical symbol for phosphorus).
'in' indicates putting letters inside.
'sill' placed around 'p' is 'spill'.
'over'+'spill'='OVERSPILL'
Can you help me to learn more?
(Other definitions for overspill that I've seen before include "Excess liquid" , "Surplus population moving elsewhere" , "for people moving out of slums?" , "Excess; surplus (population)" , "excessive amount" .)