/jif'kl/, /jaf'kl/, /j*-fi'kl/ (obsolete) To cancel or annul something. "Why don't you jfcl that out?" The fastest do-nothing instruction on older models of the PDP-10
happened to be JFCL, which stands for "Jump if Flag set and then CLear the flag"; this does something useful, but is a very fast no-operation if no flag is specified. Geoff Goodfellow, one of the jargon-1 co-authors, had JFCL on the licence plate of his BMW for years. Usage: rare except among old-time PDP-10 hackers.