This is the 59th most frequent Japanese word.
気
"気" (ki) means "spirit," "energy," "mood," or "feeling."
In this sentence, '気' is used in the expression '気をつけて', which means 'take care' or 'be cautious'. It refers to one's attention or awareness.
気をつけてください。
Please be careful.
Here, '気' refers to one's mental or emotional state, indicating a feeling of relief.
彼の優しさで気が楽になった。
His kindness eased my mind.
In this context, '気' denotes a person's inclination or mood, implying a change in preference.