Etymology Dictionary

SAD,  heavy, serious, sorrowful.  (E.)   'Sadde, tristis;' Levins.   M. E. sad, with very various meanings; Halliwell explains it by 'serious, discreet, sober, heavy (said of bread), dark (of colour), heavy, solid, close, firm (said of iron and stone).'   The W. sad means 'firm, steady, discreet;' and may have been borrowed from E. during the M. E. period.   β. But the oldest meaning is 'sated.'   Thus, in Layamon, 20830, we have 'sad of mine londe' = sated, or tired, of my land.   Hence seem to have resulted the senses of satisfied, fixed, firm, steadfast, &c.; see examples in Stratmann and in the Glossary to Will. of Palerne, &c.   The mod. E. sad is directly from the sense of sated, tired, weary.—A. S. sæd, sated, satiated; Grein, ii. 394. + O. Sax. sad, sated. + Icel. saddr, old form saðr, sated, having got one's fill. + Goth. saths, full, filled, sated. + G. satt, satiated, full, satisfied, weary.   γ. All from the Teut. type SADA, sated, Fick, iii. 318.   Cognate words are found in Lithuan. sotus, satiated; Russ. suitost’, satiety; Lat. satur, sated, also deep-coloured (like E. sad-coloured), well filled, full, sat, satis, sufficiently; all from a base SAT, with the sense of 'full' or 'filled.'   See Satiate, Satisfy.   ¶ In no way connected with set, which is quite a different word; nor with Lat. sedare, which is allied to E. set.   Der. sad-ly, -ness.   Also sadd-en, verb, from M. E. sadden, to settle, confirm, P. Plowman, B. x. 242; cf. A. S. gesadian, to fill (Grein), A. S. sadian, to feel weary or sad, Ælfred, tr. of Boethius, cap. xxxix. § 4.