The use of hot to mean excellent or fashionable dates to the mid-19th century. From H.W. Shaw’s 1866 Josh Billings, Hiz Sayings:
I dropt tu sleep, az a snoflake dus on the buzzum ov a silvery Lake, (i have a faint idee that this laste sentense, for lovlaness, kant be beat, handy.) I dreamed a good-sized, hot dream.1
And there is this quotation from 1869, found in Pauli Murray’s Proud Shoes:
Our hides are all stamped with the name of our firm on them and they look hot.2
Where exactly this metaphorical sense of the word comes from is uncertain. There are many slang and metaphorical senses of hot and teasing out which ones stem from which others is next to impossible. But it seems likely that this sense comes from the idea that something new is literally hot, still warm from process of manufacture, hot off the press, etc.
1Josh Billings, Josh Billings, Hiz Sayings (New York: Carleton, 1866), 172-73.
2Historical Dictionary of American Slang, v. 2, H-O, edited by J.E. Lighter (New York: Random House, 1997), 170.
Copyright 1997-2015, by David Wilton