Sentence:  The problem gives us a number of <WSD>tablespoons</WSD> of cooking oil and asks us to convert this amount into milliliters. We are also told that one <WSD>tablespoon</WSD> equals 3 teaspoons, but this is a relationship between two units, not an actual measurement. 
Meaning of the word marked with <WSD> tags:  A unit of volume, the value of which varies regionally; "in the US: three teaspoons or roughly 15 ml; in Britain and Canada: exactly 15 ml; in Australia: four teaspoons or 20 ml".