Sentence:  We went into Mrs. Monmouth 's library , which had low bookshelves all along the walls , and above them a Modigliani portrait , a Jackson Pollock twelve <WSD>feet</WSD> long , and a gorgeous Miro with a yellow background , that looked like an inscription from a Martian tomb . 
Meaning of the word marked with <WSD> tags:  a linear unit of length equal to 12 inches or a third of a yard