What year did the word "hot" first take on the meaning of a man or
woman being sexy? e.g. "She's really hot!" I could not find this in a
slang dictionary from 1987.

Hello kjr291,

The online version of the Oxford English Dictionary (available through
some library databases), in its Draft Additions of March 2005 for the
entry "hot", says:

"slang (orig. U.S.). Of a person (originally a woman): sexually attractive."

The OED's first citation is:

"1926 New Republic 17 Feb. 350/2 If you've forgotten your mythology,
Aphrodite -- more widely known as Venus -- was the hot momma of
goddesses."

This entry includes "Cf. RED-HOT a. 2a."  The "red-hot" entry says, in
relevant part:

"Of persons: ... outstanding, uninhibited, lively, sexy, passionate;
esp. in phr. red-hot momma ...."

Its first citation for "red-hot mama" is from 1926, the same year as
the New Republic citation.

In short, it appears that "hot" first took on the meaning of "sexy" in
or about 1926.

- justaskscott

How old is the term "hot" as in sexy?

William Shakespeare loved to play with words. In A Midsummer Night's
Dream Theseus speaks these oxymoronic words (Act V, Scene I):
"A tedious brief scene of young Pyramus
And his love Thisby; very tragical mirth.'
Merry and tragical! tedious and brief!
That is hot ice and wondrous strange snow."

Here is what the Etymology Online Dictionary says:

"Hot-blooded "passionate" (1598) is a relic of medieval physiology
theory. The association of hot with sexuality dates back to 1500."

"In heat":  "Meaning "sexual excitement in animals" is from 1768."  

"Hot" in the sense you mean may not be in a slang dictionary because
it is not considered to be slang. In my Webster's dictionary, the
seventh definition of "hot", "lustful, lascivious", is not noted as
being slang, also not in my 1953 Webster's Collegiate Dictionary,
where the second definition is:  "characterized by violent activity,
emotion or passion; as: a ardent; fiery. b violent; raging. c excited;
urgent. d. lustful. e kindled with eager desire; as, hot for reform."

Most people reading "kindled with eager desire" probably don't think
about reform, and probably didn't 50 years ago, but Webster's left
more to one's imagination in those days.

Hmmm?  I wonder what Shakespeare meant by "wondrous strange snow"?
Myoarin

"Hmmm?  I wonder what Shakespeare meant by "wondrous strange snow"?"

Oh, that bawdy Bard!

I won't bother to check my previous source, this is obviously the
first usage of "snow"  for cocaine  ...  Or don't you think so,
Badger?

"I won't bother to check my previous source, this is obviously the
first usage of "snow"  for cocaine  ...  Or don't you think so,
Badger?"

Hmmm, don't know. A Midsummer Night's Dream is a comedy about romance
and sex. But there are so many hallucinatory aspects to it, one can't
be sure. Shakespeare was the master of the double entendre.

Quite, indeed; he could whip off "wondrous strange snow" before anyone
knew what he was talking about, except Thisby, maybe.

Justaskscott,
It's hard to argue with OED.

I wonder where etymonline got its information?

Myoarin

Myoarin,

The Etymology Online Dictionary refers to "sexuality," not to
sexiness.  Someone can be sexual / have sexuality without being sexy,
no?

:-)

- justaskscott

Justaskscott,
Thanks, maybe  - if you and the big book say so.
When I associate hot with sexuality, I infer sexy, but that just may be my 
male mind's slipping into lower gear on sighting the first syllable
and no longer being able to deal with the finer meaning of a
five-syllable word.  :-9

Anyway, thanks again.
Myoarin