adj a private signal, word, or phrase, which must be given in order to pass a sentry; a watchword.
2. countersign ·adj the signature of a secretary or other officer to a writing signed by a principal or superior, to attest its authenticity.
3. countersign ·vt to sign on the opposite side of (an instrument or writing); hence, to sign in addition to the signature of a principal or superior, in order to attest the authenticity of a writing.