Plan 9 from User Space's /usr/local/plan9/src/cmd/dict/rev.awk 

NF == 2	{
		printf "%s\t%s\n", $2, $1
	}
NF != 2 {
		print "ERROR " $0
	}

Space Glenda

Copyright © 2005 Lucent Technologies, Russ Cox, MIT.
See license for details.