Ethelred

"member of a noble family," Old English æðling, from æðel "noble family, race, ancestry; nobility, honor," related to Old English æðele "noble," from Proto-Germanic *athala- (cognates: Old Frisian edila "(great-)grandfather," Old Saxon athali "noble descent, property," Old High German adal "noble family"), which is perhaps from PIE *at-al- "race, family," from *at(i)- "over, beyond, super" + *al- "to nourish." With suffix -ing "belonging to." A common Germanic word, cognates include Old Saxon ediling, Old Frisian etheling, Old High German adaling.

"counsel, advice," Old English ræd "advice, counsel," from Proto-Germanic *redin (source also of Old Saxon rad "advice, counsel, help, advantage," Old Frisian red "council, advice," Dutch raad "advice, counsel," German Rat "advice, counsel," Old Norse rað "advice, consideration, remedy, power; marriage"), from the source of read (v.), which originally meant "to advise, counsel." A very frequent word in Old English and early Middle English, falling from literary use 17c. until revived somewhat in 19th century archaic and poetic diction.

The verb read in the already obsolete sense ' counsel, advise,' was much affected by Spenser, and in the early modern and ME. spelling rede which he used has likewise been much affected by his archaizing imitators; but there is no historical ground for a difference in spelling. [Century Dictionary]

*rē-, Proto-Indo-European root meaning "to reason, count;" a variant of PIE root *ar-, also arə-, "to fit together." 

It forms all or part of: Alfred; arraign; arithmetic; Conrad; dread; Eldred; Ethelred; hatred; hundred; kindred; logarithm; Ralph; rate (n.) "estimated value or worth;" rathskeller; ratify; ratio; ration; read; reason; rede; rhyme; riddle (n.1) "word-game;" rite; ritual.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit radh- "to succeed, accomplish;" Greek arithmos "number, amount;" Latin reri "to consider, confirm, ratify," ritus "rite, religious custom;" Old Church Slavonic raditi "to take thought, attend to;" Old Irish im-radim "to deliberate, consider;" Old English rædan "to advise, counsel, persuade; read;" Old English, Old High German rim "number;" Old Irish rim "number," dorimu "I count."