### Clue: Diamond edging for rich decoration on vehicle (7)
### Answer: RHOMBUS 
 ### Explanation: Definition: Diamond
 **1st and last letters of**(edging for) "rich" + OM(abbrev. for the Order of Merit, an honour/decoration given by the monarch of the Commonwealth) + BUS(a large vehicle for people transport).
… a pattern made up of rhombi.