In the Penguin translation of Catullus two words are left untranslated. ‘Pedicabo et irrumabo vos’, writes the poet of his foes Furius and Aurelius and ‘pedicabo et irrumabo vos’ is how it stays in Peter Whigham’s English version. The first word means ‘I will bugger you’. When the present writer turned as a schoolboy to Lewis and Short’s Latin dictionary he learnt that pedicare meant only to perpetrate some nameless ‘unnatural vice’. The second word is also often translated as ‘to bugger’. The same Lewis and Short gives an even vaguer definition ‘to treat in a foul or shameful manner’. The real meaning of irrumare is one of the revelations in Mr J N Adams’s masterful new guide, The Latin Sexual Vocabulary, to which perplexed schoolboys and scholars will henceforth be able to turn for unerring advice on these erstwhile delicate matters.

Irrumare turns out to be one of those words with no exact English equivalent. It signifies the act of fellatio from the active rather than the passive point of view. This may seem a trivial matter but it was important for the Romans, to whom sexual vocabulary mattered in the general language of status and power politics. Mr Adams’s book is not a complete analysis of Roman sexual politics. It does not do for Latin culture what Kenneth Dover’s new classic, Greek Homosexuality, does for Greek. But as a linguistic guide it is a start.

A proper understanding of irrumare, for example, makes clear some otherwise rather obscure jokes, such as at Catullus 74 where a certain Gellius puts a stop to his uncle’s moralising about his illicit affairs by having an affair with the uncle’s wife. The uncle is so ashamed that he dare not speak: even if Gellius were to irrument him, he wouldn’t say a word, writes Catullus. Understanding this as ‘to bugger’ him, as Whigham does, it is an extra insult. Understanding it as to force him to submit to fellatio, it is a strong paradoxical joke.

Not that Adams makes it too easy for schoolboy seekers after truth. He sticks to many of the conventions of sex and the classics, ie that meanings should be mostly circumlocutory and if possible themselves also in Latin. Just as mentula, the common Latin for penis, is translated in Lewis and Short as membrum virile, so irrumare, even in Adams, turns up as mentulam in os inserere. The ignorant seeker after titillation, even with Adams in his school library, will still be denied.

It is one of those nice linguistic ironies that English should have attempted to make sex respectable by clothing it in Latin words – penis, vagina, pudenda – that classical Latin speakers would have considered old-fashioned and quaint if they had understood them at all. The Romans had no such specific, scientific words for individual sex organs and functions. They had no scientific need for them. What they did have was a range of sexual vocabulary – of every possible metaphorical and physical shade – which until Mr Adams’s book I had not seen brought together in one place.

The Latin words for doves and sparrows, ploughshares and plectums, ladles and lizards, poles, spears, snakes, turtles and cabbages all stood in for the common-or-garden mentula which Cicero, amongst others, considered too crude to use for the male sex organ. On the female side the choice was only a little less colourful. Cunnus was the standard word for the female’s sexual apparatus: but it was supplemented by the words for piglet (particularly used by women themselves), meadow and pasture, caves and ditches, doors, domestic altars, bags and ovens.

There is an agreeable lack of class barriers in Latin obscenity. From gentlemen like Catullus and Caesar to the meanest Pompeian graffiti-chalker, the words are more or less the same. In one of his more famous dirty poems Catullus calls the word of a rival poet cacata carta – shit-sodden sheets: and in a slogan from Pompeii, long anticipating the F-plan diet, an anonymous graffitist scratched the well-turned thought caca bene irrima medicos – shit well, stuff the doctors.