Sentence:  Venice also needed <WSD>alum</WSD> for trade, since it was the point of departure for overland transportation of <WSD>alum</WSD> to southern Germany and its cloth-manufacturing Free Cities. 
Meaning of the word marked with <WSD> tags:  An astringent salt, usually occurring in the form of pale crystals, much used in the dyeing and tanning trade and in certain medicines, and now understood to be a double sulphate of potassium and aluminium (K<sub>2</sub>SO<sub>4</sub>.Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>.24H<sub>2</sub>O). (from 14th c.)