$line = " Jack and jill went up the hill to fetch a pail of water. Jack fell down and broke his crown and jill came tumbling after.";

$newline = $line;        ## MAKE A COPY OF THE LINE

@wordlist = (hill,pail,water,down);   # THE LIST OF WORDS TO SEARCH FOR

## FOR EACH WORD IN THE WORDLIST -- FOOTNOTE THE WORD
for ($i=0; $i < @wordlist; $i++)
{
    $currword = $wordlist[$i];
    $newline =~ s/(\b$currword(?:ed|ing|al)?\b)/\\footnote\{$1 $hash{lc($1)}{explanation}\}/im;
}