这应该给你“提姆”：

$syllable[0] = $syllableInitials[0][0] . $syllableMedials[2] . $syllableFinals[0];

在代码中，您只指向[0]中的另一个数组；

Array (
     [0] =>**Array ( [0] => t )**
     [1] => Array ( [0] => d ) 
     [2] => Array ( [0] => ch )
)

所以你有两个选择。。
第一：

$syllable = array("","","");

$sql = "SELECT characters FROM syllableInitials";
$result = $conn->query($sql);

$syllableInitials = array();

while ($initial = mysqli_fetch_row($result)) {
    $syllableInitials[] = $initial[0];
}
$syllableMedials = array("a", "o", "i");
$syllableFinals = array("m","s","d");

$syllable[0] = $syllableInitials[0] . $syllableMedials[2] . $syllableFinals[0];

echo "Syllable is: <b>" . $syllable[0] . "</b>";

第二：

$syllable = array("","","");

$sql = "SELECT characters FROM syllableInitials";
$result = $conn->query($sql);

$syllableInitials = array();

while ($initial = mysqli_fetch_row($result)) {
    $syllableInitials[] = $initial;
}
$syllableMedials = array("a", "o", "i");
$syllableFinals = array("m","s","d");

$syllable[0] = $syllableInitials[0][0] . $syllableMedials[2] . $syllableFinals[0];

echo "Syllable is: <b>" . $syllable[0] . "</b>";

因为$initial是一个数组，并且有一个元素，所以您可以执行以下操作：

$syllableInitials[] = $initial[0];

但更好的解决方案是将pdo与其pdostatement:：fetchcolumn函数一起使用。
例如：

$syllable = array("","","");

$options = array(
    PDO::ATTR_PERSISTENT => true,
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
);

$dbh = new PDO('mysql:dbname=dbname;host=127.0.0.1', 'username', 'password', $options);

$sth = $dbh->prepare('SELECT characters FROM syllableInitials');
$sth->execute();

$syllableInitials = array();

while ($initial = $sth->fetchColumn()) {
    $syllableInitials[] = $initial;
}
$syllableMedials = array("a", "o", "i");
$syllableFinals = array("m","s","d");

$syllable[0] = $syllableInitials[0] . $syllableMedials[2] . $syllableFinals[0];

echo "Syllable is: <b>" . $syllable[0] . "</b>";