Sentence:  He found the blend "tomax" in "a collection of gratulatory verses presented by the President and Fellows of Harvard College 1 to the new King, George III," dated 1761. A note by the owner of the volume explains the word as a combination of tomahawk and axe: "It is a <WSD>portmanteau</WSD> word, which must have been as clear to the average reader in England of 1761 — as clear to George III himself - as brillig and slithy would have been to us, had not Humpty Dumpty kindly explained them." 
Meaning of the word marked with <WSD> tags:  A portmanteau word.