Translation:This kanji dictionary is very thick.
There is more than one word for thick, of course. You'll often hear 厚い(あつい)コート, when referring to a thick winter coat.
Duolingo, come on. We're almost at the end of the course here. There is no reason you should be using so little kanji. This sentence is hard to look at! Look at all the じs and しs in a row! If you're gonna write sentences using kana alone, at least put spaces between the words. I have a copy of ファイナルファンタジーIV on the スーパーファミコン and all of the dialog is in kana, but at least there are spaces! So even Japanese media uses spaces when there are no kanji
I agree using more kanji would help with readability of the sentences. Using kanji would also help to better clarify homonym conflicts, other than relying on context alone to solve said issue. For example in this sentence the "あつい", they want is "あつい" as in ( thick / "厚い" ) and not "あつい" as in ( hot / "暑い" ). One could argue that context makes the choice obvious and you can't refer to a dictionary as hot, but the sentence could be interpreted as "the kanji dictionary is very hot", "hot" as in popular. We only have so much context to work with after which we have to make a best guess. This is where kanji could help considerably. I think kanji should be interleaved with the lessons a bit more and done at gradually increasing rate as the user progresses through each lesson.