The phrase "become indistinct" refers to something that has lost its clarity or definition. There are various synonyms that can be used to convey a similar meaning, including blurred, obscure, hazy, foggy, fuzzy, unclear, vague, uncertain, and ambiguous. These words suggest that something is difficult to distinguish or interpret, and that its features or details are uncertain or imprecise. Whether referring to a visual image, a sound, or a concept, these synonyms all convey the idea that something has become obscure or less distinct over time, making it harder to discern or understand.