Much of the endowment is earmarked towards specific ends. It is not a slush fund for discretionary spending.

Earmarked implies discretionary so it is discretionary

Most of it is not discretionary, no matter what words random Internet commenters use to describe it.

I am replying to the GP. GP must be mistaken. It was Harvard’s choice to operate this way financially

I understand. I am saying they are correct that much of Harvard's endowment is not discretionary, even if they accidentally used a term that implies that it is.

That's not what discretionary means in this context. The funds having been originally earmarked at the discretion of the originator, means they are no longer available for any purpose at the discretion of the trustee, meaning they are no longer discretionary. You are confusing the funds having once been earmarked at someone's discretion for their being discretionary, which they haven't been since the point when they were earmarked at the originator's discretion.