Daughter is one of the oldest words in the language, and the gh in the middle is the fossil of a sound English no longer makes. Old English had dohtor, where that h stood for a rasping consonant like the ch in Bach. The sound died out in English between about 1400 and 1600, but the spelling had already been fixed by then, so the letters stayed on as silent freight. The same is true of night, light, thought and plough.
The word goes back beyond Germanic to a common Indo-European ancestor, with cousins in Sanskrit, Greek, Armenian, Lithuanian and Old Church Slavonic — one of the small set of kinship terms shared across the whole family. Curiously it was lost in both Celtic and Latin, which each built their own word instead. The modern English spelling settled in the 1500s in southern England, long after the pronunciation it records had gone.
daughter (n.) Middle English doughter , from Old English dohtor "female child considered with reference to her parents, " from Proto-Germanic *dokhter , earlier *dhutēr (source also of Old Saxon dohtar , Old Norse dóttir , Old Frisian and Dutch dochter , German Tochter , Gothic dauhtar ), from PIE *dhugheter (source also of Sanskrit duhitar- , Avestan dugeda- , Armenian dustr , Old Church Slavonic dušti , Lithuanian duktė , Greek thygater ). The common Indo-European word, lost in Celtic and Latin (Latin filia "daughter" is fem. of filius "son"). The modern spelling evolved 16c. in southern England. In late Old English also "woman viewed in some analogous relationship" (to her native country, church, culture, etc.). From c. 1200 of anything regarded as feminine, considered with respect to its source. Related: Daughterly . Daughter-in-law is attested from late 14c. (see in-law ). Earlier was sonnes wif (early 14c.), earlier still snore , from Old English snoru , cognate with Old Norse snör , archaic German Schnur , from PIE root *snuso- (source also of Sanskrit snuṣa- , Greek nyos , Latin nurus (itself the source of Old French nuere , Spanish nuera ), Old Church Slavonic snŭcha , Russian snocha ), which is of uncertain origin.
daughter came in through Old English, and its spelling follows that family's conventions.
How that family writes these sounds
| a vowel that runs longer than it should, before nothing you can hear | gh — silent, or said as flight, night, daughter, enough |
Placing it without the spelling
| the body, the farm, the weather, the family, the hundred commonest words | Old Englishknee, sheep, wind, daughter |
Old English in the spelling guide · guess another word's family