Old English rædan (West Saxon), redan (Anglian) "to advise, counsel, persuade; discuss, deliberate; rule, guide; arrange, equip; forebode; read, explain; learn by reading; put in order" (related to ræd, red "advice"), from Proto-Germanic *raedanan (cf. Old Norse raða, Old Frisian reda, Dutch raden, Old High German ratan, German raten "to advise, counsel, guess"), from PIE root *re(i)- "to reason, count" (cf. Sanskrit radh- "to succeed, accomplish," Greek arithmos "number amount," Old Church Slavonic raditi "to take thought, attend to," Old Irish im-radim "to deliberate, consider"). Words from this root in most modern Germanic languages still mean "counsel, advise."
Sense of "make out the character of (a person)" is attested from 1610s. Connected to riddle via notion of "interpret." Transference to "understand the meaning of written symbols" is unique to Old English and (perhaps under English influence) Old Norse raða. Most languages use a word rooted in the idea of "gather up" as their word for "read" (cf. French lire, from Latin legere). Read up "study" is from 1842; read out (v.) "expel by proclamation" (Society of Friends) is from 1788. read-only in computer jargon is recorded from 1961.