A common synonym for "ball of thread" is "skein." A skein is a length of yarn or thread, loosely coiled and often sold in a hank or bundle. Another synonym is "spool," which refers to a cylindrical object used for winding and storing thread or yarn. "Bobbin" is another term for a small spool used in sewing machines. A "wad" of thread refers to a tangled or bunched-up mass of thread that is difficult to work with. Lastly, a "hank" is another term for a skein, referring to a length of yarn or thread that is coiled into a loop and sold tied with a knot.