The Oxford Dictionary of Difficult Words

We all know what the words cat and dog and mother and tree mean. What we really need is a dictionary that helps us with the tough words, like elucubrate , or demesne , or cynosure . True, a standard dictionary can bail us out when we run across a tough word at home or in a library. But we often read elsewhere--in a doctor's waiting room or on a plane, or while on vacation. What do we do then?