mould

One strand comes through Middle English molde/moulde and Old French modle, from Latin modulus, giving us the sense of a cast or shape. A second strand comes from Middle English mowlde, tied to moulen (“to grow mouldy”), from Old Norse mygla, tracing back through Proto-Germanic *muglōną to Proto-Indo-European *mewk- (“slick, soft”). A third strand comes from Old English molde, meaning earth or soil.

These three separate words for shaping, fungal growth, and soil all collapsed into one spelling and sound over time, even though they never shared a root.

The fungal-growth sense is distantly related to muck and meek, both traced back to the same Proto-Indo-European root *mewk- meaning 'slick, soft.'