countersign vs validate

countersign

• To add a second signature to a document, affirming the validity of the signature of another person. 

• To sign on the opposite side of (a document). 

• A second signature added to a document to affirm the validity of the signature of the first person. 

• The response to a sign or signal. 

validate

• To check or prove the validity of; verify. 

• To have its validity successfully proven. 

• To render valid.