a character of special significance in an organism. Such characters are used in a system for determining the identity of an organism on the basis of the presence or absence of a succession of characters. Usually such keys are DICHOTOMOUS (2); that is to say, at each step there is a choice between two possibilities. Keys, however, may have more than two characters at each step and there is a gradual elimination of absent characters until identification is made.
However, on the second time round, she came upon a low curtain she had not noticed before, and behind it was a little door about fifteen inches high: she tried the little golden key in the lock, and to her great delight it fitted!