"Absolute necessity" refers to something that is extremely important and cannot be done without. It is a crucial requirement or essential item that is vital for a specific purpose or situation. Full definition
These are absolute necessities when someone decides to enter this wonderful industry. (remonline.com)
In all cases experimentation should not be done unless absolute necessity can be demonstrated and all alternative possibilities have been excluded after serious consideration. (religion-online.org)
Here, the evidence revealed no such absolute necessity, and any records claimed to be subject to solicitor ‑ client privilege should not be disclosed. (slaw.ca)