The adjective "most plumbean" is a fairly obscure term often used in literary contexts to describe a character or situation that is peculiar, eccentric, or outlandish. Synonyms for this term include "whimsical," "quirky," "offbeat," "unconventional" and "idiosyncratic." Other similar terms that come to mind include "kooky," "eccentric," "odd," "zany," and "off-center." Each of these synonyms can bring a slightly different connotation or degree of intensity to the meaning, but all capture the sense of something being unusual or unexpected in a creative way. These terms are frequently used in artistic or literary circles to describe a work or personality that stands out from the norm.