You can use rindex to find the last occurrence of a substring in a string: 
#!/usr/bin/perl
use warnings;
use strict;

my @lexikon = sort { length $b <=> length $a } qw/ own known /;
my $word = "unknown";
print rightside($word), "\n";

sub rightside {
    my $word   = shift;
    my $length = length $word;
    for my $l (@lexikon) {
        return $l if $length - length $l == rindex $word, $l;
    }
    return q();
}

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لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: Longest String Matching by choroba
in thread Longest String Matching by Dr Manhattan

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