Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
sex [sɛks] n (gender) пол; (lovemaking) секс
both sexes о́ба по́ла
to have sex with sb переспа́ть*(perf) с кем-н
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.