He always enjoys minimising his contributions, even though the project couldn't have been done without him.

minimising 是动词 minimise 的现在分词形式。minimise 由词根 mini（表示"小"）和动词后缀 -ise（表示"使...化"）组成，意思是"使最小化、极力降低"。在这里表示"刻意淡化、轻描淡写"的意思。