To obtain by paying. Also a grip that lets force be applied — the same word for buying and for holding on.
Old French porchacier (to pursue eagerly, to seek to obtain): por- (Latin pro-, forth) + chacier (to chase, to hunt); a purchase was first a pursuit, and only later the settled exchange of money for the thing pursued.
To obtain by paying, or to gain a grip that lets force be applied. The pursuit buried in the root connects both senses: something not yet held is chased until it is.