purchase

Jennifer WeinerのFly Away Homeを読んでいます。
“Ow,” he said, startled. “Ow, shit!” His legs were splayed out in front of him, his socks drooping, his pants legs riding up, exposing his hairy calves. She grabbed his hand to pull him upright but couldn’t get enough purchase with her silly high-heeled shoes, so she wound up on top of him, her chest pressed against his, both of them on the wintry, wet ground, laughing until tears ran from her eyes. She knew it was ridiculous, and that poor Richard’s pants were soaked and probably ruined, but the day had been so terrible, and it felt good to laugh.
"purchase" は誰でも知っている単語ですが、購入するとか買う（そしてその名詞）の意味しか知らないので上の "purchase" の個所の意味が分かりません。辞書を見ます。
　 ・Oxford English Dictionary: A hold or position on something for applying power advantageously, or the advantage gained by such application.: the horse's hooves fought for purchase on the slippery pavement
・Cambridge English Dictionary: a firm hold that allows someone or something to be pulled or lifted without sliding or falling: Dancers use a special powder on their shoes to help them get a better purchase on the floor.
"purchase" にこんな意味もあるのを知りませんでした。