Sentence:  The weather of the summer of 1863 was, if we include the above four months, not remarkable; but June and September had exceedingly fine weather, while July and August were very unhealthy, being warmer than usual and much damper—that is, <WSD>sultry</WSD>. 
Meaning of the word marked with <WSD> tags:  Hot and humid. (from late 16th c.)