When is a Newt called an eft? This is the common newt, found in my pond in my garden in Southern England. very cute...
This, by contrast, is the Hong Kong Newt - Paramesotriton hongkongenis.
A newt is a type of salamander in the subfamily Pleurodelinae, and to answer my own question is also called eft during its juvenile phase.
Here is tiny, teeny weeny eft of a HK newt in a river pool.
The Old English name of the animal was efte, and this became euft, evete, or ewt(e). The initial 'n' was added from the indefinite article 'an' by provection (juncture loss) ("an eft" -> "a n'eft" -> ...) by the early 15th century.
The form 'newt' appears to have arisen as a dialectal variant of eft in Staffordshire, but entered Standard English by the Early Modern period, and was used by Shakespeare in Macbeth - remember, as the one of the witches begins the spell "Eye of newt, and toe of frog,Wool of bat, and tongue of dog, Adder's fork, and blind-worm's sting, Lizard's leg, and howlet's wing,--For a charm of powerful trouble,Like a hell-broth boil and bubble."
The regular form eft, now only used for newly metamorphosed specimens, survived alongside newt, especially in composition, the larva being called "water-eft" and the mature form "land-eft" well into the 18th century, but use of the simplex "eft" as equivalent to "water-eft" has been in use since at least the 17th century.
Other names translate literally as "lizard-badger" or "distaff-like lizard" Newts are also known as Tritones (viz., named for the mythological Triton) in historical literature, and "triton" remains in use as common name in some Romance languages, in Greek, in Romanian, Russian, and Bulgarian.
OK, language lesson over!