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";
}
[download]

is one interesting interpretation, producing:

definedWord:    defined
time:   defined
system: defined
Bareword "foo" not allowed while "strict subs" in use at (eval 4) line
+ 1.

foo:    UNdefined
BEGIN:  defined
syntax error at (eval 6) line 1, at EOF

if:     defined
-e:     defined
syntax error at (eval 8) line 1, near "{ lt"

lt:     defined
goto:   defined
last:   defined
[download]