Other forms: moulded, moulding, moulds
Mould is the fuzzy grey-green stuff that grows on damp things and old food. The furry patch on bread left too long in the bag, black speckles creeping up the bathroom wall, white bloom on a forgotten jar of jam.
It is also a second, unrelated thing spelled the same way: a hollow shape you pour something soft into so it sets hard — a jelly mould, a chocolate mould, the steel moulds a factory presses plastic parts in. From that comes the verb. You mould clay into a bowl, and a coach moulds a group of strangers into a team. Americans write both words as mold. Mouldy is the adjective for the fungus, and mouldy bread is the loaf you throw out. Gardeners have a third use: leaf mould, the dark crumbly earth that dead leaves turn into.
1nounmouldA soft fuzzy growth of fungus on damp surfaces or old food.
“There was mould along the window frame where the damp got in.”
synonyms: mildew
2nounhollowA hollow container that something soft or liquid is poured into and left to harden in that shape.
“Pour the mixture into the mould and leave it in the fridge overnight.”
3verbmaterialTo shape a soft material by hand or in a form; to shape the way a person or group turns out.
“The sergeant moulded the new recruits into something like a unit.”
4noundarkDark crumbly earth made of rotted leaves.
“He dug a barrowload of leaf mould into the vegetable bed.”
mould is a fungus.
Also accepted in games: mold
The mould you pour things into came through Middle English molde, mould or cast, from Old French modle, from Latin modulus. That chain belongs to the shaping mould, the container that gives a thing its form. The fuzzy mould on your bread is a separate word that happens to have landed on the same spelling.
Latin
modulus
Old French
modle
Middle English
molde — mould, cast
English, today
mould
Via Middle English molde (“mould, cast”) and Old French modle, from Latin modulus.
Etymology from Wiktionary, CC BY-SA