zoo
One three letter word relating to anger and ending with O is ego.
Some three letter words that end with "o" are:agoegoduowhowootootwoboopoomooloogoo
tools
who
The three-letter Gershwin is "Ira." The "o" is probably incorrect.
too
the letter three and oclock
ore
Ono
oak oak
dog cow mop cot
It could be rot.