أُخَرَ is the feminine plural corresponding to «أُخْرَى», meaning “other.” The book includes it under ʿadl + adjectival status.
مِنْ أَيَّامٍ أُخَرَ
Translation: from other days.
مِنْ: preposition. أَيَّامٍ: genitive noun with kasra. أُخَرَ: adjective qualifying «أَيَّامٍ», itself grammatically genitive but marked with fatḥa as a diptote.
The phrase occurs in Qurʾān 2:184, within «فَعِدَّةٌ مِنْ أَيَّامٍ أُخَرَ».