(n.) Habitual silence, or reserve in speaking.

brachylogy briefness brusqueness compactness compendiousness conciseness concision crispness curtness dumbness economy economy of words instantaneousness laconicalness laconicism laconism littleness lowness muteness obmutescence pauciloquy pithiness pointedness quietness quietude reserve sententiousness short time shortness silence sparingness of words speechlessness succinctness summariness swiftness taciturnity terseness transience unloquaciousness untalkativeness wordlessness