Kerttu is a Finnish variant of Gertrude. Gertrude originates in Germanic languages and means "the strongest spear". It has been a popular feminine given name within royalty throughout history, including Gertrude of Bavaria, the Queen of Denmark, Gertrude of Hohenburg, the Queen of the Romans, and others. Gertrude was also the name of Hamlet's mother in William Shakespeare's play. In the United States it is a rather unusual name these days.