Tafsir of Az-Zukhruf 43:75

"They will not be granted a respite [from it]" (i.e., it will not be lightened for them, taken from the expression "the fever fatrat [abated] from him" when it subsides slightly). The root, in any of its forms, indicates weakness absolutely.

"And they therein" (i.e., in the punishment; ‘Abdullah recited: "therein," meaning in Hell) "will be plunged into despair" (mublisun).

"Despairing" from the intensity of the affliction. Al-Raghib said: Al-iblas is the sorrow that befalls one due to the intensity of despair. From this, "Iblis" is derived, according to some. Since one who is mublis (in despair) often remains silent and forgets what concerns him, it is said that one is mublis when he falls silent and his argument is severed. End quote. Al-iblas here has been interpreted as silence and the severance of one's argument.