The original Constitution never used the words "slave" or slavery," but it sure did talk about them ...
In the Constitutional Convention, the Northern and Southern states agreed to a number of compromises about slavery. But in the Constitution itself, you will not find the words "slave" or "slavery" anywhere (at least, not until the Thirteenth and Fourteenth Amendments of the 1860's).
Constitutional Convention, 1787
For example, it used euphemisms like "service or labour," or the "importation of such persons"
Instead, you will find a number of diplomatically-worded euphemisms that were meant to ease the consciences of Northerners on this issue, such as the ones that follow. Instead of "slavery," they say "service or labour." Instead of the "slave trade," they say the "importation of such persons." And instead of just saying "slaves," they say "three-fifths of all other persons" (which I will elaborate on later here.)
Slave dance to banjo, 1780's