Which of the following describes a delicate thread or fabric?

The term "gossamer" specifically refers to something that is both delicate and lightweight, often describing a fine, filmy substance or a very sheer fabric. In literary contexts, it can evoke a sense of fragility and ethereality, making it particularly suited to describe threads or fabrics that are almost translucent and insubstantial. This aligns perfectly with the question's requirement for a description of a delicate thread or fabric.

The other options do not convey the same meaning. "Harrow" relates to agriculture, specifically a tool used in farming. "Exegesis" pertains to a critical interpretation or explanation of textual content, often used in literary or theological contexts. "Gambol" refers to the act of skipping or frolicking, which does not relate to fabric or thread at all. Thus, "gossamer" stands out as the correct choice due to its associations with delicacy and lightness.