definiens
Pronunciation: /dɪˈfɪnɪɛnz/
noun ( plural definientia)
- a word, phrase, or symbolic expression used to define something, especially in a dictionary entry, or introducing a word or symbol into a logical system by providing a statement of its meaning. Contrasted with definiendum.

Origin:
late 19th century: from medieval Latin, 'defining', present participle of definire (see define)