the.com/mould

means A furry fungal growth that spreads on damp or decaying organic matter, or (in British spelling) the hollow shape you pour something into to give it form.

from These are actually two different words that collided in spelling. The fungus sense traces to Old English 'mowlde', related to Old Norse 'mygla' (to grow musty), itself tied to an ancient root about softness or crumbling — the same family that gives us 'mellow'. The shape/form sense comes via Old French 'modle' or 'molle' from Latin 'modulus', a little measure — the same root behind 'module' and 'model'. So one mould quietly ruins your bread, while the other shapes your chocolate bunny, and they only met by coincidence of spelling.