The Collaborative International Dictionary of English v.0.48:
Briefness \Brief"ness\ (br[=e]f"n[e^]s), n. The quality of being brief; brevity; conciseness in discourse or writing. [1913 Webster] BrierWordNet (r) 3.0 (2006):
briefness n 1: the temporal property of being very short 2: the attribute of being brief or fleeting [syn: brevity, briefness, transience]