Duḥkha (/ˈduːkə/; Sanskrit: दुःख, Pali: dukkha) "suffering", "pain", "unease", or "unsatisfactoriness", is an important concept in Buddhism, Jainism and Hinduism. Its meaning depends on the context, and may refer more specifically to the "unsatisfactoriness" or "unease" of craving for and grasping after transient 'things' (sense objects, including thoughts), expecting pleasure from them while ignorant of this transientness. In Buddhism, dukkha is part of the first of the Four Noble Truths and one of the three marks of existence. The term also appears in scriptures of Hinduism, such as the Upanishads, in discussions of moksha (spiritual liberation).

While the term dukkha has often been derived from the prefix du- ("bad" or "difficult") and the root kha ("empty," "hole"), meaning a badly fitting axle-hole of a cart or chariot giving "a very bumpy ride," it may actually be derived from duḥ-stha, a "dis-/ bad- + stand-", that is, "standing badly, unsteady," "unstable."

Duḥkha (Sanskrit: दुःख; Pali: dukkha) is a term found in the Upanishads and Buddhist texts, meaning anything that is "uneasy, uncomfortable, unpleasant, difficult, causing pain or sadness". It is also a concept in Indian religions about the nature of transient phenomena which are innately "unpleasant", "suffering", "pain", "sorrow", "distress", "grief" or "misery". The term duḥkha does not have a one-word English translation, and embodies diverse aspects of unpleasant human experiences. It is often understood as the opposite of sukha, meaning lasting "happiness," "comfort" or "ease".

The word has been explained in recent times as a derivation from Aryan terminology for an axle hole, referring to an axle hole which is not in the center and leads to a bumpy, uncomfortable ride. According to Winthrop Sargeant,

The ancient Aryans who brought the Sanskrit language to India were a nomadic, horse- and cattle-breeding people who travelled in horse- or ox-drawn vehicles. Su- and dus- are prefixes indicating good or bad. The word kha, in later Sanskrit meaning "sky," "ether," or "space," was originally the word for "hole," particularly an axle hole of one of the Aryan's vehicles. Thus sukha ... meant, originally, "having a good axle hole," while duḥkha meant "having a poor axle hole," leading to discomfort.

Joseph Goldstein, American vipassana teacher and writer, explains the etymology as follows:

The word dukkha is made up of the prefix du- and the root kha. Du- means "bad" or "difficult". Kha means "empty". "Empty", here, refers to several things—some specific, others more general. One of the specific meanings refers to the empty axle hole of a wheel. If the axle fits badly into the center hole, we get a very bumpy ride. This is a good analogy for our ride through saṃsāra.

However, according to Monier Monier-Williams, the actual roots of the Pali term dukkha appear to be Sanskrit दुस्- (dus-, "bad") + स्था (sthā, "to stand"). Regular phonological changes in the development of Sanskrit into the various Prakrits led to a shift from dus-sthā to duḥkha to dukkha.