Webster's Revised Unabridged Dictionary · 1913

Muggy

Muggy (mug"gy) , adjective

[Compare Icelandic mugga mist, mugginess. Compare 4th Mold.]

1.
Moist; damp; moldy; as, muggy straw.
2.
Warm, damp, and windless; uncomfortably hot and humid; sultry; as, muggy air, weather.