Not the one that means "to buy." But the one I've come across countless times without ever really registering and that I came across again in an article that read:
"Desperate to hold on to something, to gain some purchase, Clive started to keep a journal"
Here's that definition of "purchase," per Webster's New World College Dictionary":
"a firm hold applied to move something mechanically or to keep from slipping b) any apparatus for applying such a hold."
Now I know.