Rav Haim Vital (1543-1620) writes that his teacher, the Arizal (Rav Yishak Luria of Safed, 1534-1572), made a point of never verbalizing the names of the angels, even over the course of study. For example, Rav Haim writes, the Arizal would refer to the "Sar Hapenim" (angel that serves as "minister of interior") as "Mem Tet," rather than verbalize the entire name. The reason for this practice is that when an angel hears his name mentioned, he thinks that he is being summoned, and he becomes anxious. When he then finds out that his anxiety was for naught, he might become resentful of the person who made him nervous, and cause him harm, Heaven forbid.

This does not, however, apply to angels whose names are commonly used here on earth, such as Michael, Gabriel, Raphael, Azriel, and Malkiel.

The Arizal was especially adamant that one should never verbalize the complete name of the Satan. He would refer to the Satan by saying the letters "Samech Mem," rather than articulating his name. Rav Haim Vital writes that on one occasion he was speaking to somebody at nighttime and mentioned Satan’s name, and the next morning, when he went to the Arizal’s home, the Arizal looked at his forehead and said, "At night you transgressed the prohibition of ‘Ve’shem Elohim Aherim Lo Tazkiru’ (‘Do not mention the name of other gods’ – Shemot 23:13)." The Arizal admonished Rav Haim in very harsh terms never to mention the name, especially at nighttime, when the Satan has power which could be reinforced by the mention of his name, such that he can succeed in causing the person to sin, Heaven forbid. Likewise, one should refrain from verbalizing the complete name of Satan’s "wife," who should be referred to as simply, "Li," rather than with her complete name.

This applies to all languages. As such, one should refrain from saying the word "D-e-v-i-l," or the parallel Spanish term, especially during the nighttime hours, as this could arouse and empower Satan.