Semordnilap

my $words = set slurp("unixdict.txt").lines;

my @sems = gather for $words.flat -> $word {
    my $drow = $word.key.flip;
    take $drow if $drow ∈ $words and $drow lt $word;
}

say $_ ~ ' ' ~ $_.flip for @sems.pick(5);

Output:

abut tuba
avid diva
bard drab
loot tool
part trap