Merriam-Webster's Collegiate® Dictionary, 11th Edition
BACKPACK
I. noun
Date: 1914
1. a load carried on the back, a camping pack (as of canvas or nylon) supported by a usually aluminum frame and carried on the back, knapsack , a piece of equipment designed for use while being carried on the back,
II. verb
Date: 1927
transitive verb to carry (food or equipment) on the back especially in hiking, intransitive verb to hike with a backpack, backpacker noun