my %sth;
foreach my $tab (@checklists)
{
    # BTW, this SQL may be better written:
    #     select 1 from $tab where word = ?
    # if all you're testing for is existence...
    $sth{$tab} = $dbh->prepare("SELECT word from $tab where word = ?");
}
# later...
foreach my $tab (@checklists)
{
    $sth{$tab}->execute($word);
    my $ret = $sth{$tab}->fetchrow_hashref();
}