mould: English has three words mould. By some way the oldest is ‘earth, soil’ [OE], which comes ultimately from the Indo-European base *mel-, *mol-, *ml- ‘grind’ (source also of English meal ‘flour’, mill, etc). Moulder  may be derived from it. Mould ‘form’  is assumed to come from Old French modle ‘form, shape, pattern’.
This was descended from Latin modulus ‘small measure’ (source of English module), a diminutive form of modus ‘measure’ (source of English mode, model, etc). Mould ‘fungus’  appears to have originated as an adjective, meaning ‘mouldy’. This in turn was an adjectival use of the past participle of a now obsolete verb moul ‘go mouldy’, which was borrowed from an assumed Old Norse *mugla. => meal, mill, molar, moulder; mode, model, mood