Thīna

Thīna (Sanskrit styāna|स्त्यान​; थीन) is a Buddhist term that is translated as "sloth". Thīna is defined as sluggishness or dullness of mind, characterized by a lack of driving power. In the Theravada tradition, thīna is said to occur in conjunction with middha (torpor), which is defined as a morbid state that is characterized by unwieldiness, lack of energy, and opposition to wholesome activity. The two mental factors in conjunction are expressed as thīna-middha (sloth-torpor).

Thīna is mentioned in the Pali canon as:
 * One of the five hindrances to meditation practice (in combination with middha, i.e. as sloth-torpor)
 * One of the fourteen unwholesome mental factors within the Theravada Abhidharma teachings
 * Closely related to the Sanskrit term kausīdya (spiritual sloth), that is identified as one of the twenty secondary unwholesome factors within the Mahayana Abhidharma teachings

Explanation
Bhikkhu Bodhi explains:

"Sloth is sluggish or dullness of mind. Its characteristic is lack of driving power. Its function is to dispel energy. It is manifested as the sinking of the mind. Its proximate cause is unwise attention to boredom, drowsiness, etc.

Sloth and torpor (middha]) always occur in conjunction, and are opposed to energy (viriya). Sloth is identified as sickness of consciousness (citta-gelanna), torpor as sickness of the mental factors (kayagelanna). As a pair, they constitute one of the five hindrances, which is overcome by initial application (vitakka)."

The Atthasālinī (II, Book I, Part IX, Chapter II, 255) states about sloth and torpor: “Absence of striving, difficulty through inability, is the meaning.” We then read the following definitions of sloth and torpor:

"The compound “sloth-torpor” is sloth plus torpor; of which sloth has absence of, or opposition to striving as characteristic, destruction of energy as function, sinking of associated states as manifestation; torpor has unwieldiness as characteristic, closing the doors of consciousness as function, shrinking in taking the object, or drowsiness as manifestation; and both have unsystematic thought, in not arousing oneself from discontent and laziness (or indulgence), as proximate cause."

Nina van Gorkom explains: "When there are sloth and torpor there is no energy, no vigour to perform dāna, to observe sīla, to listen to Dhamma, to study the Dhamma or to develop calm, no energy to be mindful of the reality which appears now."