Where does “sla” come from?

sla (Middle English) comes from Old English slāh, from Proto-Germanic slaihwō, from Proto-Indo-European (s)leh₃y- — blueish.

Ancestry of “sla”, step by step

StepLanguageWordMeaning
1Old Englishslāhsloe
2Proto-Germanicslaihwō—
3Proto-Indo-European(s)leh₃y-blueish
Every word from Proto-Indo-European (s)leh₃y- →Every word from Proto-Germanic slaihwō →Every word from Old English slāh →