The scientist became a defector and developed advanced weapons for the enemy country.

defector 是由动词 defect（叛逃、背叛）加上名词后缀 -or（表示"做...的人"）构成的名词，指"叛逃者、变节者"。defect本身由前缀 de-（表示"离开"）和词根 fect（来自拉丁语 facere，意为"做"）组成，字面意思是"背离原来的行为"。