I assume he meant this site:
goo辞書 - 国語・英語・四字熟語・中国語のオンライン辞書
(1) input the word you want to check
(2) choose the dictionary
国語 : Japanese dictionary in Japanese
英和 : English-Japanese dictionary
和英 : Japanese-English dictionary
(3) search option
で始まる : begins with (the word you are searching)
で終わる : ends with...
に一致する : exact match
を含む : including ...
を説明文に含む : including... in the definition
(4) hit the 辞書検索 (dictionary search) button
then you'll get the result.
This is another dictionary site which is very useful.
株式会社アルク
(1) input the word you want to check (either in English or in Japanese)
(2) hit 英和・和英 button
(3) the result will be shown.
This website is really good as it does not just show the words but many phrases and examples including the word you are looking up.
*note: When inputting Japanese word, you have to use Japanese characters (kanji, kana, katakana). No Japanese in romaji (Roman alphabets).
e.g.
apple, 林檎、りんご、リンゴ are OK.
ringo is NG.