starch

nouns

a complex carbohydrate found chiefly in seeds, fruits, tubers, roots and stem pith of plants, notably in corn, potatoes, wheat, and rice; an important foodstuff and used otherwise especially in adhesives and as fillers and stiffeners for paper and textiles
is derived from
a commercial preparation of starch that is used to stiffen textile fabrics in laundering
is a type of (narrower)
a substance prepared according to a formula
"the physician prescribed a commercial preparation of the medicine"

verbs

stiffen with starch
"starch clothes"
is a type of (narrower)
make stiff or stiffer
"Stiffen the cream by adding gelatine"