Summary “There are 150 words in Catullus which occur once only in his writings, and of these more than 70 per cent are rare in the whole of Latin literature, and more than 90 per cent do not occur in Vergil at all” – writes J. Whatmough in his work Poetic, Scientific, and other Forms of Discourse, Berkeley and Los Angeles, 1956, 41. It is necessary to distinguish between genuine and apparent once-words. The true once-word is a coinage that never recurs; the number of the true once-words is exceedingly small. Catullus’ once-words were well known, but not in writing. Theoretically one would expect such words to be polysyllabic; so are the comic jawbreakers of Aristophanes which fit the pattern of his verse so well. The hapax legomena of Catullus are not genuine once-words of the spoken language, but they are vulgar and in some contexte obscene. We can, therefore, regard them as taboo words. They occur sometimes in similes; cf. Poems 17, 23, 25, 97. In my paper I would like to analyse some vulgar hapax legomena of Catullus.