At length Meaning, Definition & Usage

  1. adverb in a lengthy or prolix manner
    lengthily.
    • the argument went on lengthily
    • she talked at length about the problem

WordNet

Definitions
  1. . (a) At or in the full extent; without abbreviation; as, let the name be inserted at length. (b) At the end or conclusion; after a long period. See Syn. of At last, under Last.

Webster 1913