Sentence:  In America alone, people spent $170 billion on “direct marketing”—junk mail of both the physical and electronic varieties—last year. Yet of those who received unsolicited adverts through the post, only 3% bought anything as a result. If the bumf arrived electronically, the take-up rate was 0.1%. And for online adverts the “conversion” into sales was a <WSD>minuscule</WSD> 0.01%. 
Meaning of the word marked with <WSD> tags:  Very small, tiny.