Mean hail storm (7)
I believe the answer is:
average
'mean' is the definition.
(I know that mean can be written as average)
'hail storm' is the wordplay.
'hail' becomes 'ave' (greeting in Latin).
'storm' becomes 'rage' (synonyms).
'ave'+'rage'='AVERAGE'
(Other definitions for average that I've seen before include "Mediocre, commonplace" , "just like any other" , "Fair to middling" , "Mean, so-so" , "'Medium, middling (7)'" .)