my @terms = ('lymph', 'lymph node');
my @text = ('right lymph node', 'lymph fluid');

# create a regexp that will match the longest
# string first and capture the string that matched
my $words = '\b(' .
    join('|',
    sort { length $b <=> length $a } @terms) .
    ')\b';

for my $text (@text) {
    if ($text =~ /$words/) {
        print $text, ": matched => ", $1, "\n";
    }
}