Despite the difficulties, he kept his word and finished the project on time.

kept 是动词 keep 的过去式，keep 的基本意思是"保持、保留"。 his 是代词 he 的所有格形式，表示"他的"。 word 在这里指"诺言、承诺"，而不是字面意义的"单词"。 kept his word 是一个固定短语，意思是"信守诺言、履行承诺"。