A fictitious**** animal having a lion's head and a fish's tail.

It is a compound word, comprising the French word for sea (mer-) with "lion". However, it is totally unrelated to the sealion and should not be confused with seals and sea otters either.

The Merlion is the national symbol of Singapore. It has its roots in local legend, when a prince of the Sri Vijaya empire named Sang Nila Utama first set foot on a small island then known as Temasek or "sea". Upon seeing a lion*, he renamed the island Singapura, which in Sanskrit means Lion (singa) City (pura). The name was later shortened to Singapore.

The lion head of the Merlion represents how Singapore acquired its name; the tail of the fish, that Singapore was originally known as Temasek, the "sea". Another meaning is that Singapore's success (the lion) was established upon marine trade in the past (as Singapore was well-placed to be a port and the center for import/export activities). Mr. Fraser Brunner, who was a member of the Souvenir Committee and the curator of the Van Kleef Aquarium, came up with the design for the Merlion, which became the emblem of the Singapore Tourism Board from 1964 to 1997.

The famous Merlion statue standing currently at the mouth of the Singapore River was designed by Mr. Kwan Sai Kheong, then Ambassador to the Philippines and Vice Chancellor of the University of Singapore. It was sculpted by a local craftsman Mr. Lim Nang Seng, completed in August, 1972, and installed by Mr. Lee Kuan Yew, the first Prime Minister of Singapore, on his birthday, 15th September, 1972.

A replica stands on Sentosa Island. At 37 metres, it is the tallest structure on the resort island and has 320 scales sculpted from glass-reinforced concrete, which glows in different colours once it is dark. It also beams lasers from its eyes, which makes them seem to pulsate with a greenish light. It is a sight to behold at night.

*One would be curious (and rightly so) as to why a lion, normally a creature of open plains, would be found in a tropical rainforest. It is likely that the animal was a tiger. Since neither Sang Nila Utama nor his men had ever seen a lion before (this point is part of the legend** passed down), it is probable that they made a mistake***. It is also probable, however, that perhaps they did see an Asiatic lion, one of the relatives of the protected species now living in India's Gir Forest.

**The legend stated that Sang Nila Utama turned to his men and inquired about the strange animal that he had just seen. The men did not know***, but a wise old man remarked that he had heard of this animal before, the fabled Singa, which would bring good fortune to whomever saw it.

***Although it seemed that Sang Nila Utama and his men had never seen a lion before, yet it cannot be concluded that he had made a mistake. They probably should have seen and known what a tiger looked like, as tigers used to be a common predator in Southeast Asian forests and was a feared enemy. This assumption stands on the premises that Sang Nila Utama was not short-sighted and that his men were not trying to curry his favour...

****The Merlion was created in the late 1900s. It does not have roots in Malay legends, and therefore there is no Malay name for it. It is a totally modern fictitious animal.
This is in response to a question by Cletus the Foetus:

Is this what the Singaporeans call it? Does it have an Indic or Malay name?