Etymology: Old English sǽl masculine and feminine < Germanic type *sǣli-z , apparently a substantive use of the adjective found in Gothic sêl-s good (whence sêlei goodness), Old Norse sǽll happy (whence sǽla weak feminine, sǽld strong feminine, happiness); in West Germanic outside English preserved only in derivatives, Old Saxon sâlig , Old High German sâlîg (see seely adj.), Middle High German sâllîche fortunately, Old Saxon sâlda , Old High German sâlida happiness (see selth n.). An ablaut-variant *sōl- occurs in Old English sél adverb: see etymological note to sele adj.

Etymology: Apparently an inferred positive of the comparative and superlative forms seler adj., selest adj., in sense 1 influenced semantically by seely adj. (although compare usell adj. and Old Icelandic sæll happy: see sele n.).The form selen apparently shows an instance of nunnation, a very common feature of the language of the Caligula manuscript of Laȝamon’s Brut, which has not been satisfactorily explained. The following isolated modern Scots example, a rendering of Psalm 122:6, probably shows a rare use as adjective (in sense ‘blessed, happy’) of sele n. (compare sense 1 at that entry) rather than a revival of this word:1928 T. T. Alexander Psalms in Braid Scots 19 Pray that Jerusalem may be Fu' lown, and aye be seil.