diff -r ea804c814693 -r 9abd946f990c src/Pure/Tools/dump.scala
--- a/src/Pure/Tools/dump.scala	Sat Sep 08 13:36:40 2018 +0200
+++ b/src/Pure/Tools/dump.scala	Sat Sep 08 14:30:31 2018 +0200
@@ -208,7 +208,7 @@
     -D DIR       include session directory and select its sessions
     -O DIR       output directory for dumped files (default: """ + default_output_dir + """)
     -R           operate on requirements of selected sessions
-    -W SECONDS   delay for cleaning of already dumped theories (0 = disabled, default: """ +
+    -W SECONDS   watchdog timeout for PIDE processing (0 = disabled, default: """ +
       Value.Seconds(Thy_Resources.default_watchdog_timeout) + """)
     -X NAME      exclude sessions from group NAME and all descendants
     -a           select all sessions