http://www.webshas.org/dibbur/clean.htmClean LanguageClean Language and R' Yochanan Ben Zakkai
Euphemisms
Foul Speech
Regarding sexual relations: Ketuvot 8b
Use of foul language when discussing a topic which is naturally involved in such things: Pesachim 3a-b
Use of apparently foul speech, where clean speech could have been substituted: Rosh HaShanah 4a
Substituting cleaner language in the public Torah reading: Megillah 25b
Seriousness
Connection between foul language and poor lineage: Pesachim 3b
Use of disgusting words in ordinary [non-holy] speech: Pesachim 3a
Choice of extra words vs. foul speech: Pesachim 3a-3b
Divine Punishment of Children, where the Parents are guilty of foul speech: Ketuvot 8b
Foul Speech causes Divine Termination of a 70-year Prescription for Life: Ketuvot 8b
Lishna Mialya Nakat - Using Clean/Superior Language
"Asher Lo Tahor [Not Pure]" in place of "Tamay [Impure]": Pesachim 3a
"Asiyyas Tzerachim [Doing one's Needs]" to refer to sexual relations: Pesachim 109b, 110a
"Atzmo [Self]" rather than refer directly to Heaven in a negative way: Berachot 14b
"Aveirah [Transgression]" to refer to Sexual sin: Rosh HaShanah 17a
"Avdo [one's eved]" referring to paying someone for illicit sexual relations with his female eved; the Talmud refers to it as occurring between the two avadim: Temurah 29a, 30a
"Bait Yazek" instead of "Bait Yazek," place of chaining, where the witnesses who testified on the New Month stayed, if they arrived on Shabbat: Rosh HaShanah 23b
"Cheder/Prozdor/Aliyah [Various Rooms]" in discussing sections of the female genitalia: Niddah 17b
"Davar Acher [Another Matter]" for sexual relations: Berachot 8b, Yevamot 109a
"Davar Acher [Another Matter]" for Pig: Shabbat 129b, Pesachim 3b; Kiddushin 39b
"Davar Acher [Another Matter]" for tzaraat: Shabbat 129b, Pesachim 112b
"Davar Gadol [A Large Thing]" for consumption of a Limb of a Live Animal: Gittin 7a
"Dibbur [Speech]" referring to inter-gender isolation: Ketuvot 13a, 16a
"Dog" in place of "Donkey": Pesachim 49b
"Eating" in place of sexual relations: Ketuvot 13a
"Gani [Sleeping]" in place of "Buried": Moed Katan 25a
"HaKol [All]" in place of Ra [Evil]: Berachot 11b [Note that this is a rejected explanation]
"Lechem [Bread]" in place of sexual relations: Niddah 17a
"Keres [Stomach]" in place of the groin area: Niddah 13b
"Midi [Something]" for Seed: Shabbat 140b
"Milsa [Something]" in place of Death: Shabbat 136a; Moed Katan 18a, 21a, 26b
"MiVarech" [Blesses] HaShem, in place of the opposite: Pesachim 93b
"Moshav [Seat]" in place of "Merkav [Riding]" for a female rider: Pesachim 3a
"Or" [Light] in place of Laylah [Night]: Pesachim 2a-3a
"Regel [Foot]" in place of reference to genitalia: Yevamot 103a
"Rok [Saliva]" and "Peh [Mouth]" regarding semen inside a woman: Niddah 16b
"Shechitah [Ritual Slaughtering" in place of "Nechirah [Violent Murder]": Pesachim 49b