This Halacha is an excerpt from our Sefer
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Not to say the word Chametz:
Some write that one is not to mention the word “Lechem” or “bread” on Pesach, and rather one is to say the word Chametz. Some however write that the Rebbe negated the use of the word Chametz when in reference to actual existing Chametz. [However, certainly the word Chametz may be used in general reference such as in Halacha and Torah learning.] Some would avoid even saying the last name of a person if it has reference to Chametz [such as the Bagel family].
 Otzer Minhagei Chabad 26; Nitei Gavriel 1 40:6
 Sefer Tishbi “Davar”; Mishnas Yaakov 446; Heichal Bracha [Komrana] Riei 12:21
The reason: As Chametz on Pesach is considered like idolatry and one may not think of other G-ds or recite their names. [Heichal Bracha ibid]
 Otzer ibid; Hiskashrus 38:13
 Pashut, otherwise it would be forbidden to learn most chapters in Shulchan Aruch Hilchos Pesach and many Sichas of the Rebbe dealing with Pesach. The Rebbe himself said the word Chametz in many Sichas during Pesach.
 Minhag Admurei Bubuv brought in Nitei Gavriel ibid