dear (adj.) Look up dear at Dictionary.com
Old English deore "precious, valuable, costly, loved, beloved," from Proto-Germanic *deurjaz (source also of Old Saxon diuri, Old Norse dyrr, Old Frisian diore, Middle Dutch dure, Dutch duur, Old High German tiuri, German teuer), of unknown etymology. Used interjectorily since 1690s. As a polite introductory word to letters, it is attested from mid-15c. As a noun, from late 14c., perhaps short for dear one, etc.