Short answers, pulled from the story.
Joseph Goldstein explains that the word duhkha derives from an Aryan metaphor describing a cart wheel with an axle hole sitting off-center. This physical flaw creates a bumpy and uncomfortable ride for anyone traveling inside the chariot.
Dukkha-dukkha refers to physical suffering including birth, aging, illness, and dying. Viparinama-dukkha describes the frustration of disappearing happiness when pleasant experiences cease. Sankhara-dukkha indicates the unsatisfactoriness of changing and impermanent things lacking any inner core.
The Tattvartha Sutra provided detailed explanations of duhkha as an authoritative Jain scripture from the second century. This text outlines how suffering functions within Jain metaphysical traditions and philosophical frameworks regarding karma and existence.
Modern scholars emphasize that suffering remains too limited a translation for such a complex concept found in Pali texts. They prefer terms like anxiety, distress, or unsatisfactoriness because all feelings remain dukkha due to being impermanent conditioned phenomena incapable of lasting satisfaction.
Verse 6.20 of Shvetashvatara Upanishad contains references to duhkha in contexts of moksha and bhakti. It denotes distress within the context of spiritual pursuit and liberation through knowledge of Atman.