At length is a phrase that indicates a detailed discussion of a topic or a lengthy explanation of something. There are several synonyms for the phrase that can be used interchangeably depending on the context of the sentence. Some of the synonyms for at length include extensively, thoroughly, in-depth, exhaustively, comprehensively, at great length, and in detail. These synonyms can be used to convey the idea of discussing something at a greater length or giving more information. It is essential to choose the right synonym that fits the context and the tone of the sentence to avoid confusion or ambiguity.