Sentence:  Economics is a <WSD>messy</WSD> discipline: too fluid to be a science, too rigorous to be an art. Perhaps it is fitting that economists' most-used metric, gross domestic product (GDP), is a tangle too. GDP measures the total value of output in an economic territory. 
Meaning of the word marked with <WSD> tags:  In a disorderly state; chaotic; disorderly.