1 [noncount] : the time when something begins : BEGINNING — usually + of
They awaited the commencement of the trial.
It's the first attempt at peace since the commencement [=start] of hostilities.
2 US : a ceremony during which degrees or diplomas are given to students who have graduated from a school or college
the week before commencement [=graduation]
A poet will speak at the commencement.
— often used before another noun
a commencement speech/address/ceremony