Etymology Dictionary

SOOTH,  adj., true; sb., truth.  (E.)   The adjectival sense is the older one.  M. E. soth (with long o), adj., true; Pricke of Conscience, 7687.  Commoner as a sb., meaning 'the true thing,' hence 'the truth;' Chaucer, C. T. 847.—A. S. sóð, adj., true (very common); Grein, ii. 460.   Hence sóð, neuter sb., a true thing, truth; id. 462.  The form sóð stands for sanð*, the n being lost before the aspirate, as in tóð, a tooth, which stands for tanð*; the loss of n causes the o to be long. + Icel. sannr (for sanðr). + Swed. sann. + Dan. sand.   β. All from Teut. base SANTHA, true; Fick. iii. 318.   And again SANTHA is certainly an abbreviation for ASANTHA, orig. signifying 'being,' or 'that which is,' hence that which is real, truth; a present participial form from the ✔AS, to be.   The same loss of initial a occurs in the Lat. -sens as found in præ-sens (stem præ-sent-), preserved in E. pre-sent; and again in the Skt. satya, true (put for as-ant-ya*); so also we have G. sind = Lat. sunt = Skt. santi, they are, all answering to Aryan as-anti.  In the Gk. ἐteόs, true, not only this initial a but also the following s has been lost, so that ἐteόs (for ἀσ-ετεός) represents only the portion -ooth of the E. word.  Hence Curtius says of ἐteόs that 'the root is ες, to be [Aryan as].  The meaning "true," "real," appears already in the Skt. participle sat, the shorter form for sant = (a)sant (Lat. præ-sent-).'   γ. Hence we conclude that the very interesting word sooth meant orig. no more than 'being,' and was at first the present participle of AS, to be.   See Are, Essence, and Sin.   Der. for-sooth, = for a truth, A. S. for sóð, as in 'wite þú for sóð' = know thou for a truth, Ælfred, tr. of Boethius, lib. ii. pr. 2, cap. vii. § 3.   Also sooth-fast, true (obsolete), from A. S. sóðfæst, Grein, ii. 463, where the suffix is the same as in stead-fast and shame-fast (now corrupted to shame-faced).   And see sooth-say, and soothe.