Article IV, section 2.
"No Person held to Service or Labour in one State, under the Laws thereof, escaping into another, shall, in Consequence of any Law or Regulation therein, be discharged from such Service or Labour, But shall be delivered up on Claim of the Party to whom such Service or Labour may be due."
They were squeamish about using the word "slave", and so they didn't use it. Nonetheless, everyone knew to what Article IV, Section 2 referred.
Additionally, Lincoln said he would support the addition of a 13th amendment that went like this:
No amendment shall be made to the Constitution which will authorize or give to Congress power to abolish or interfere, within any State, with the domestic institutions thereof, including that of persons held to labor or service by the laws of said State.
Notice again they were squeamish about using the word "slave"?
No rational person “enshrines” a term or concept that they are too “squeamish” to utter out loud. Slavery was not enshrined in the Constitution (but I think I see why you feeeeeeel that it is).