Where does “hairbrained” come from?

hairbrained (English) comes from English Hair, from Middle English hēr, from Old English hēr, from Proto-West Germanic *hēr, from Proto-Germanic hē₂r, from Proto-Indo-European ḱe, from Middle English kyt, from German kitt — to bend; curve; arch; vault; to bow, bend, arch,...

Ancestry of “hairbrained”, step by step

hairbrained traces back through two separate lines of ancestry.

via English Hair

StepLanguageWordMeaning
1EnglishHairA pigmented filament of keratin which grows from a follicle on the skin of humans and other mammals
2Middle Englishhēra hair
3Old Englishhērat this place
4Proto-West Germanic*hērhere
5Proto-Germanichē₂rhere, in this place
6Proto-Indo-EuropeanḱeDeictic particle, here; Post-positional...
7Middle Englishkyt
8Germankittputty certain kinds of cement used for fixing e.g. window panes
9Old High Germankuti
10Proto-West Germanickwidugum, resin
11Proto-Germanickweduzresin
12Proto-Indo-Europeangʷet-resin, gum; to say, speak
13Proto-Indo-Europeangū-to bend; curve; arch; vault; to bow, bend, arch,...

via English brained

StepLanguageWordMeaning
1EnglishbrainedHaving a particular kind or number of brain;...
2EnglishbrainThe control center of the central nervous system...
3Middle EnglishbraynThe brain or cerebrum; the organ of thought;...
4Old Englishbræġnbrain
5Proto-West Germanic*bragnbrain
6Proto-Germanicbragnąbrain
7Proto-Indo-Europeanmregʰnomskull, brain
8Proto-Indo-Europeanmen-to think, mind; spiritual activity; to stay,...
Every word from Proto-Indo-European gū-