sub definedWord
{
    my( $word )= @_;
    return eval "use strict; my \$x= sub { $word  }; 1"
        ||  ( warn("$@\n"), $@ !~ /^Bareword/ );
}

@ARGV= qw( definedWord time system foo BEGIN if -e lt goto last )
    if  ! @ARGV;
for(  @ARGV   ) {
    printf "$_:\t%sdefined\n", definedWord($_) ? "" : "UN";
}