い adjective
ふかい
水深が急に深くなりましたね。
The water suddenly got deep, eh?
コウイチがデスクで深いため息をついてるのを見たんだけど、何かあったの？
I saw Koichi letting out a deep sigh, has something happened?
魚たちが、親や兄弟、高校時代の友人たちとの深い繋がりを保っていることが多いって、本当ですか？
Is it true that fish tend to maintain a deep connection with their parents, siblings, and high school friends?
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of deep? It's also deep.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. Because the reading sounds just like a dirty word, and there may be innocent children about, I'll let you come up with your own mnemonic for this one. Maybe someone pushes you into a deep hole that will surely kill you so you yell something out as you fall down it?