a. and adv. Forms: 1 þeosterlic (adj.), 4 þiesterliche (adv.). [f. THESTER a.: see -LY1, 2] a. adj. Dark. b. adv. Darkly.
c. 1000. Ælfric, Hom., I. 504. Þæs muntes cnoll mid þeosterlicum ʓenipum eal oferhangen wæs.
1340. Ayenb., 244. Þe clene of herte þet hier ssolle ysy him be byleaue, ac alneway þiesterliche.
