noun
weather; sky conditions
Refers to the look or state of the sky, often implying upcoming weather. Somewhat literary or old-fashioned; 天気 is more common in daily speech.
空合いが怪しいから、傘を持って行こう。
The sky looks threatening, so let's take an umbrella.
noun
course of events; situation; prospects
Figurative use: the way things are developing, like the look of the sky. Rare and somewhat literary; often replaced by 雲行き or 形勢.
交渉の空合いが悪くなってきた。
The course of the negotiations has taken a turn for the worse.
Compound of 空 (そら, 'sky') and 合い (あい, 'condition' or 'state'). The exact historical derivation is uncertain, but the word has been used since at least the Edo period.