'starch-forming' is a compound of 'starch' and 'forming'. 'starch' originates from Old English, specifically the word 'stearc', where it meant 'stiff'. 'forming' comes from 'form', which originates from Latin, specifically the word 'forma', where it meant 'shape'.

'starch' changed from Old English 'stearc' through Middle English forms (e.g. 'sterch'/'starch') and became the modern English word 'starch'. 'form' passed from Latin 'forma' into Old French 'forme' and Middle English before becoming the modern English 'form'; the -ing suffix is from Old English/Germanic gerundial/participial formation.

Initially, 'starch' referred to 'stiffness' (the property), but over time it came to denote the carbohydrate substance we now call 'starch'. 'form' originally meant 'shape' and later developed the verbal sense 'to give shape to' or 'to produce', which underlies the modern participial adjective 'forming'.