He was designated as the temporary team captain in the game.

designated 是动词 designate 的过去分词形式。designate 由前缀 de-（表示"完全、彻底"）和词根 sign（标记）加上动词后缀 -ate 组成，意思是"指定、指派"。designated 在句中表示被动，意思是"被指定的"。