Beach behind you, grand (8)
I believe the answer is:
thousand
'grand' is the definition.
(I know that grand can be written as thousand)
'beach behind you' is the wordplay.
'beach' becomes 'sand'.
'behind' is a charade indicator (letters next to each other).
'you' becomes 'thou' (historical second person pronoun).
'sand' after 'thou' is 'THOUSAND'.
(Other definitions for thousand that I've seen before include "Cardinal" , "Grand" , "Numeric value of kilo" , "Figure" , "Ten hundreds" .)