Rhombus (7)
I believe the answer is:
lozenge
'rhombus' is the definition.
(I know that rhombus can be written as lozenge)
This is the entire clue.
(Other definitions for lozenge that I've seen before include "Medicinal sweet" , "Rhombus; tablet" , "Medicinal tablet" , "Diamond shape; throat sweet" , "Diamond-shaped sweet" .)