That horse is acting too lively for me to bet on it.
Koichi and Viet came into the office in high spirits.
The boy left for his trip in high spirits.
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means courage so the verb version is what happens when you have lots of it. Someone with courage is probably the kind of person to be lively and to be encouraged.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
Who is the one person who always seems to be encouraged and excited? Isabel (いさ)! She's so positive and always cheers everyone, including herself, up.