Nikkhepakaṇḍa

Abhidhammapiṭaka · Dhammasaṅgaṇī · Vol. 34 · Section 798

[798] Therein, what is dullness (thīna)? That which is indisposition of the mind (citta), unwieldiness, drooping, sagging, sluggishness, being sluggish, the state of being sluggish, dullness, being dull, the state of the mind's being dull — this is called dullness.

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.