The Collaborative International Dictionary of English v.0.48:

Sooth \Sooth\ (s[=oo]th), a.; also adv. [Compar. Soother
   (s[=oo]th"[~e]r); superl. Soothest.] [OE. soth, AS.
   s[=o][eth], for san[eth]; akin to OS. s[=o][eth], OHG. sand,
   Icel. sannr, Sw. sann, Dan. sand, Skr. sat, sant, real,
   genuine, present, being; properly p. pr. from a root meaning,
   to be, Skr. as, L. esse; also akin to Goth. sunjis true, Gr.
   'eteo`s, Skr. satya. [root]9. Cf. Absent, Am, Essence,
   Is, Soothe, Sutee.]
   1. True; faithful; trustworthy. [Obs. or Scot.]
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            The sentence [meaning] of it sooth is, out of doubt.
                                                  --Chaucer.
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            That shall I sooth (said he) to you declare.
                                                  --Spensser.
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   2. Pleasing; delightful; sweet. [R.]
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            The soothest shepherd that ever piped on plains.
                                                  --Milton.
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            With jellies soother than the creamy curd. --Keats.
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