• 協力きょうりょく — cooperation
• 協会きょうかい — association / organization
• 協議きょうぎ — discussion / negotiation
• 協定きょうてい — agreement / pact
• 協同きょうどう — collaboration / joint effort
• 協業きょうぎょう — collaboration / partnership

The kanji 協 combines elements implying strength and union. It symbolizes combining power or intentions — ten people putting their thoughts or energy together. It’s used in many modern compound words that involve cooperation or group effort.