Where does “half-identical” come from?

half-identical (English) comes from English identical, from English -ál, from English aldehyde, from German Aldehyd, from Latin alcohol, from Andalusian Arabic كُحُول, from Arabic كحل, from Arabic كُحْل — kohl, antimony paste.

Ancestry of “half-identical”, step by step

half-identical traces back through two separate lines of ancestry.

via English identical

StepLanguageWordMeaning
1EnglishidenticalBearing full likeness by having precisely the...
2English-álOf or pertaining to. Adjectival suffix appended to various words, often nouns, to produce an adjective form. Often added to words of Latin origin, but used with other words also
3EnglishaldehydeAny of a large class of reactive organic...
4GermanAldehydaldehyde
5Latinalcoholkohl, collyrium, stibium; any other powder...
6Andalusian Arabicكُحُول
7Arabicكحلantimony; kohl, stibnite; black coloring of the...
8Arabicكُحْلantimony; kohl, stibnite
9Akkadianguḫlumkohl, antimony paste

via English half

StepLanguageWordMeaning
1EnglishhalfConsisting of a half; Consisting of some...
2Middle Englishhalfhalf
3Old Englishhealfside; half; partly
4Proto-Germanic*halb
5Proto-Germanichalbazhalf
6Proto-Indo-European(s)kelH-to cut; to split, to separate
7Proto-Indo-European(s)kel-to bend, crook; bent, crooked; leg, heel, knee,...
Every word from Akkadian guḫlum