1That seals itself or that may be sealed without the use of a separate sealing agent, mechanism, etc.; specifically (of a fuel tank, pneumatic tyre, etc.) able to seal small punctures automatically.
2Of an envelope or its flap: that does not require moistening in order to stick when closed.
Mid 19th century. From self- + seal.
no object To seal automatically or without the use of a separate sealing agent, mechanism, component, etc. Also with object (especially of a pneumatic tyre) to seal (a small puncture) automatically.
Late 19th century; earliest use found in Gleanings Bee Culture. From self- + seal, after self-sealed, self-sealing.