Implements hook_form_FORM_ID_alter().
function taxonomy_test_form_taxonomy_term_form_alter(&$form, $form_state, $form_id) {
$term = $form_state['controller']
->getEntity($form_state);
$antonym = taxonomy_test_get_antonym($term->tid);
$form['advanced']['antonym'] = array(
'#type' => 'textfield',
'#title' => t('Antonym'),
'#default_value' => !empty($antonym) ? $antonym : '',
'#description' => t('Antonym of this term.'),
);
}