Model/Api.php
public function deleteDictionaryItem($dictionaryId, $itemKey)
    {
        $url = $this->_getApiServiceUri(). 'dictionary/'. $dictionaryId . '/item/' . urlencode($itemKey);
        $result = $this->_fetch($url, \Zend_Http_Client::DELETE);

        return $result;
    }
public function deleteDictionaryItem($dictionaryId, $itemKey)
    {
        $url = $this->_getApiServiceUri(). 'dictionary/'. $dictionaryId . '/item/' . urlencode($itemKey);
        $result = $this->_fetch($url, \Zend_Http_Client::DELETE);

        return $result;
    }
Delete single Dictionary item

@param $dictionaryId
@param $itemKey
@return bool|mixed
@throws LocalizedException