n.
开头词

[ noun ]
the form of a word that heads a lexical entry and is alphabetized in a dictionary
<noun.communication>

main entry word \main entry word\ n.
The form of a word that heads a lexical entry and is
alphabetized in a dictionary; also called {entry word},
{headword}, and {lemma}.

Syn: citation form, entry word, headword, lemma.
[WordNet 1.5]

Note: In different languages, different wordforms, such as
cases for verbs, may be taken as the main entry word.
In English dictionaries, it is the infinitive form, but
in latin dictionaries it is usually the first person
singular present.
[PJC]