5-HT almost went by the name enteramine.
In a period between 1937 and 1940, V. Erspamer studied the enterochromaffin cells of the gut, which secrete a serum vasoconstrictor substance that he named enteramine. Erspamer detected enteramine with a color test. Its reaction with 1-nitroso-2-naphthol gave a bright violet color that he used to identify enteramine in octopod salivary glands, the thymus of some birds, and the skin of certain amphibians. Erspamer found large quantities of enteramine in the poison glands of some octopus and the stingers of wasp and bee.
Another scientist, Rapport, purified the same substance from beef blood around the same time. In 1948, Rapport published a Science paper titled "Crystalline 5-HT". In it, he wrote:
“We would like provisionally to name it serotonin, which indicates that its source is serum and its activity is one of causing constriction.” (Rapport,M.M. 1948)
"The name enteramine, indeed, though exact from a chemical point of view and in indicating the main source of 5-hydroxytryptamine, cannot be correctly applied to all known localizations of the substance; the name serotonin, in its turn, is inexact both from the point of view of the origin of the substance and from that of its action. In the sense, at least, intended by Rapport and his colleagues, it is by no means a “tonin”. (Erspamer,V. 1954)
Rapport M. M., A. A. Green and I. H. Page (1948). Crystalline Serotonin. Science 108, 329-330. 10.1126/science.108.2804.329
ERSPAMER V. (1954). Pharmacology of indole-alkylamines. Pharmacological Reviews 6, 425-487.