Flaxen thread refers to a fine, thin thread that is usually made from flax fiber. However, if you want to avoid using the same word repeatedly, there are a few synonyms that you can use instead. One alternative could be "linen thread," which is also made from flax but has a stronger connotation with the fabric it produces. Another option is "tow thread," which refers to flax fibers that are coarser than linen fibers and may be used for heavier fabrics or rope. Additionally, you could use "spun flax," which is a general term for any type of thread made from flax fibers that have gone through a spinning process.