JLPT 2 Kanji: 失

失

onyomi: シツ
kunyomi: うしな(う)、う(せる)

LOSE (something), (something is) LOST,
error, fault, disadvantage, loss, disappear

Mnemonic: It kind of looks like the 先 in 先生, so I'll remember:

The absentminded sensei is always losing シツ.

Joshi:

• 〜が失せる
• 〜を失う

Regarding 失せる:

A Google search turns up many variations of (plain form verb) + 気 + 失せる

• 読む気が失せる
• 買う気が失せる
• やる気失せる

There seem to be two ways to say that you lost your appetite:

• 食欲が失せる
• 食べる気失せる (See this post for a discussion of losing one's appetite in the summer. The post also contains 失敗, a compound meaning "failure".)

Regarding 失う:

失う is for when a person or thing loses something else. It can be a quality, an item, etc. Example sentence comes from ALC:

仕事を失う（こと）ほどストレスの大きいことは、そうそうない。

See that page for many more examples.

Compounds:

失敗 しっぱい failure.

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