Flooded area was hard (5)
I believe the answer is:
awash
'flooded' is the definition.
(synonyms)
'area was hard' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'hard' becomes 'h' (abbreviation used in pencil classifications).
'a'+'was'+'h'='AWASH'
(Other definitions for awash that I've seen before include "Flooded; about to sink" , "Letting in the sea" , "Partly under water" , "Overflowing" , "Doused in water" .)