noun.
A word, phrase, or name, usually set in boldface or other distinctive type, that serves as the heading for an entry in a dictionary, encyclopedia, or similar reference work.
noun.
A word that may be modified by an adjunct.
The Century Dictionary and Cyclopedia
noun.
A word put as a title (and printed usually in a distinctive type) at the head of a paragraph, as the words in full-face at the beginning of the several articles in this dictionary; a title-word; a word constituting a heading or a side-head.
the GNU version of the Collaborative International Dictionary of English
noun.
a word that is qualified by a modifier.
noun.
a word placed at the beginning of a line, paragraph, or short article (as in a dictionary or encyclopedia entry); the word which forms the title of an entry in a dictionary.