<input autofocus type="text" name="check" class="input-trans" placeholder="Введите перевод..." required />
<input type="button" name="word" value="<?=$row['word']?>" />
<button type="submit" name="btn" class="check"></button>
Array ( [check] => Окно [word] => [btn] => )
<form method="post" action="check/check-words.php">
<input autofocus type="text" name="check" class="input-trans" placeholder="Введите перевод..." required />
<input type="hidden" name="word" value="<?=$row['word']"?>>
<button type="submit" name="btn" class="check"></button>