companion

Companion means:

a personal advisor ,
a personal escort ,
a mentor, see mentoring ,
a moon of a planet, see satellite (astronomy) ,
the smaller component of a double star ,
the instrumental accompanist for singers or instrumental soloists, see accompaniment (music)
the article of a noun, see article (part of speech)

See also:

Wiktionary: Companion - explanations of meanings, word origins, synonyms, translations