Ｏk in my Japanese reading/writing class we have entered into topics of 話し言葉、柔らかい言葉、硬い言葉、and　書く言葉.

I've looked through my 国辞書 to see if they have any suggestions in entries, for 硬い words but I'm not seeing it. So stuff like すごくー＞とても　やっぱりー＞やはり、朝ごはんー＞朝食。(Some of that is 話し言葉）

My question is, are there any good online dictionaries or 電子辞書 dictionaries that I might now know of (and have haha) that show/suggest better words?

Thanks