靖 (jìng) is a bound morpheme (不成词语素) that appears in literary and historical compounds, typically carrying the meaning of 'pacify, stabilize' or the resulting state 'peace, tranquility'. You'll encounter it in words like 绥靖 (suí jìng, appeasement/pacification), 靖康 (Jìngkāng, a Song dynasty reign period associated with a major crisis), and 靖边 (jìng biān, to stabilize the frontier). It does not function as an independent word in modern Mandarin.