The crossword solution for the term 'LENGTHWISE THREADS' is 'WARP'. WARP threads are the lengthwise threads in a woven fabric. They are held in tension on a loom and run parallel to each other. The weft threads, which are perpendicular to the WARP threads, are woven over and under the WARP threads to create the fabric. WARP threads are usually stronger than weft threads and are often made of a different material.