• 吉きち — good luck; good omen
• 大吉だいきち — great fortune (omikuji category)
• 中吉ちゅうきち — middle fortune (omikuji category)
• 吉日きちじつ — auspicious day
• 吉報きっぽう — good news
• 吉祥きっしょう — auspiciousness; good omen
• 吉兆きっちょう — lucky sign; portent of good
• 不吉ふきつ — ill omen; unlucky

吉 combines a “top mark” above 口 (mouth), often explained as an auspicious proclamation or a ritually “good” utterance. From there comes the sense “good fortune; lucky; auspicious.” You’ll see it everywhere from shrine lots (おみくじ) to phrases like 吉日きちじつ.

Note: The on-yomi alternates between キチ and キツ in compounds (e.g., 吉報きっぽう, 不吉ふきつ). This is a common sound change for ease of pronunciation.