Short form of dictionary — values reached by name rather than by position. A named structure rather than a concept.
Latin dictionarium, a word-book, from dictio (a saying, expression), from dicere (to say); dict is the modern clipping kept where values are reached by name.
Values reached by name rather than by position, held under the same short root a wordbook has always carried. What a dict stores is retrieved by asking for it, not by counting to it.