You know how in Greek there are three different words for love depending on what exactly you mean? The English 'sexy' is similar. However, the best I can think of is illecebrosus, -a, -um. From Lewis & Short:
I.full of allurement, very enticing, attractive, seductive (ante- and post-class.): “istoc illecebrosius Fieri nihil potest,” Plaut. Bacch. 1, 1, 54: “sapor,” Prud. adv. Symm. 2, 144: “insidiae,” Amm. 30, 1.—Adv.: illĕcĕ-brōsē , enticingly, attractively.—Comp.: “agi,” Amm. 30, 5, 7 (but not in Plaut. Mil. 3, 2, 36; v. Ritschl ad h. l.).
Now, if "alluring, enticing, attractive, and seductive" isn't what I'd call "sexy", I don't know is! It has the added benefit of being "low class," i.e. it's used in pre-Classical (Plautus from the looks of it) and late Latin authors, but the stodgy "Classical Latin" foregoes it.
