dearyoudaoicibaDictYouDict[dear 词源字典]
dear: [OE] Dear is one of the English language’s more semantically stable words. By the 11th century it had already developed its two major present-day senses, ‘much-loved’ and ‘expensive’, which are shared by its Germanic relative, German teuer (Dutch has differentiated dier ‘much loved’ from duur ‘expensive’). All these words go back to a prehistoric West and North Germanic *deurjaz, whose ultimate origin is not known.

In the 13th century an abstract noun, dearth, was derived from the adjective. It seems likely that this originally meant ‘expensiveness’ (although instances of this sense, which has since disappeared, are not recorded before the late 15th century). This developed to ‘period when food is expensive, because scarce’, and eventually to ‘scarcity’ generally.
=> dearth[dear etymology, dear origin, 英语词源]
dear (adj.)youdaoicibaDictYouDict
Old English deore "precious, valuable, costly, loved, beloved," from Proto-Germanic *deurjaz (cognates: Old Saxon diuri, Old Norse dyrr, Old Frisian diore, Middle Dutch dure, Dutch duur, Old High German tiuri, German teuer), ultimate origin unknown. 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.