Dirty food alongside (6)
I believe the answer is:
grubby
'dirty' is the definition.
(similar in meaning)
'food alongside' is the wordplay.
'food' becomes 'grub' (grub can informally mean food).
'alongside' becomes 'by' (I've seen this in other clues).
'grub'+'by'='GRUBBY'
(Other definitions for grubby that I've seen before include "Dirty or unwashed, as urchin may be" , "Covered with ingrained dirt" , "Dirty, grimy" , "Squalid" , "Dirty, could do with with a wash" .)