The job became repetitive after a few weeks, with the same tasks every day.

repetitive 是形容词，来自动词 repeat（重复）加上后缀 -itive 构成。repeat 表示"重复做某事"，-itive 是形容词后缀，表示"具有...性质的"。repetitive 合起来表示"重复的、反复的"，形容某事不断重复、缺乏变化。