Sentence:  Its citizens spoke all of the world 's surviving tongues , plus a new one called Lingo , a pidgin whose vocabulary was derived from the other six and whose syntax <WSD>was</WSD> so simple it could be contained on half a sheet of paper . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)