Noun. Pseudo-nautical contraction of "list swain" (cf bosun for boat swain), being a member of a mailing list discussion group devoted to matters nautical.
"There will be a lissun gathering in Seattle to celebrate the long-awaited release of Patrick O'Brian's seafaring epic 'The Jet Black Shore'"
by Skyring August 15, 2004
by Ruff gai December 8, 2016