Unknown figure couple invested in this rare diamond (8)

18D — Unknown figure couple invested in this rare diamond (8) — SIXTIETH

• Definition
  Definition found: 'rare diamond' — The definition is the last two words — the anniversary a diamond marks. Show hint
• Indicator
  Indicator found: 'invested in' Show hint
• Operation
  'invested in' signals a container operation
• Fodder
  Fodder: 'Unknown figure couple'
• Synonym
  Synonyms spotted: 'Unknown figure' → SIXTH Show hint
• Synonym
  Synonyms spotted: 'couple' → TIE Show hint
• Assembly
  SIXTH + TIE = SIX(TIE)TH

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