What is another word for stamp approval?
Pronunciation: [stˈamp ɐpɹˈuːvə͡l] (IPA) 
The phrase "stamp approval" could be replaced with many synonyms depending on the context. If referring to formalizing or signing off on a document, one could use "endorse," "authorize," "certify," or "validate." In a more informal setting, one may use "OK," "approve," "thumbs up," or "give the green light." Other synonyms may include "sanction," "ratify," "accord," or "concur." The choice of synonym may depend on the tone and formality of the situation, as well as the type of document or action being approved. Regardless, each synonym carries the connotation of giving official or unofficial permission or support for something.
