Where does “arrow slit” come from?

arrow slit (English) comes from English arrow, from Middle English ārwe, from Old English arwe, from Proto-West Germanic *arhu, from Proto-Germanic arhwō, from Proto-Indo-European h₂érkʷo- — bow, arrow.

Ancestry of “arrow slit”, step by step

arrow slit traces back through two separate lines of ancestry.

via English arrow

StepLanguageWordMeaning
1EnglisharrowA projectile consisting of a shaft, a point and a...
2Middle EnglishārweAn arrow projectile weapon shot from a bow
3Old Englisharwearrow
4Proto-West Germanic*arhuarrow
5Proto-Germanicarhwōarrow
6Proto-Indo-Europeanh₂érkʷo-bow, arrow

via English slit

StepLanguageWordMeaning
1EnglishslitA narrow cut or opening; a slot; The opening of...
2Englishslittenpast participle of slit
3Old Englishslītanto slit, tear, rend, shiver, split, rend to...
4Proto-West Germanicslītanto tear apart
5Proto-Germanicslītanąto tear apart
6Proto-Indo-Europeansleyd-
Every word from Proto-Indo-European h₂érkʷo-Every word from Proto-Germanic arhwōEvery word from Proto-West Germanic *arhu