A sobriquet is a nickname or term of endearment given to someone instead of using their real name. It is often used to describe someone's characteristics, personality, or a notable aspect of their identity.

Private Eye, a well-known British satirical magazine, habitually referred to US President Jimmy Carter as "Hiram B Toadthrush". The name was originally chosen to epitomise an American non-entity which, as far as the outside world was concerned, was his position when he started his campaign for the presidency. After he was elected president the Eye kept this as a soubriquet for him, as they did for other public figures that they wrote about.

Henry VIII's first daughter was Mary, daughter of Catherine of Aragon (Henry's first wife). She later became Queen Mary I. Henry's second daugher was Elizabeth (who later became Elizabeth I) daughter of Anne Boleyn, Henry's second wife.

Wrong category if the "second Earth" you mean is the one a quick search found: nothing to do with speleology, but a planet orbiting a star called Gliese 581C about 20 light-years away in the constellation of Libra.

It is calculated to have a surface temperature similar to that of Earth, so amenable to life, but there the resemblance ends so far at least. The soubriquet appears to have been invented by the headline-writers of the British newspaper, The Guardian.