Sailor messed with crew before temperature drop (9)
I believe the answer is:
'drop' is the definition.
(abate can mean to drop or subside)
'sailor messed with crew before temperature' is the wordplay.
'sailor' becomes 'ab' (abbreviation for able seaman).
'messed' becomes 'ate' (mess can mean to eat in a military mess).
'with' says to put letters next to each other.
'crew before' becomes 'men' (I've seen this before. I am not sure about the 'before' bit.).
'temperature' becomes 't' (abbreviation).
Can you help me to learn more?
(Other definitions for abatement that I've seen before include "Lessening in intensity or amount" , "relief" , "mitigation" , "Subsidence" .)