Human-ish was one of the designations used for some kinds of posthumans.
In the 26th century, it was a term used to unfavourably describe people who were genetically close to humans. Like the Tylerkind, who had genetically adapted to life on the mostly-aquatic Tyler's Folly, human-ish people had slightly different, and supposedly undesirable, physiologies from the human baseline. According to Kommander Ernst Katastrophen and others, the word subhuman was a synonym.
Thus, unlike the term humanoid, human-ish was flatly derogatory. Indeed, the measurement of "human-ish-ness" was used in at least the 26th century as a means of racial suppression by the SSSSSSS. In the middle of the century, legislation by the name of the First Demographic Charter of 2537 arose which gave both power and definition to the measurement of a person's level of humanity. Bernice Summerfield found the SSSSSSS' efforts at genetic management on Tyler's Folly both laughable and worthy of her opposition. (PROSE: Down)
In contrast, in the year 5,000,000,000, Lady Cassandra cited "human-ish" among a list of names posthumans of various kinds used for themselves, alongside new humans, proto-humans and digi-humans. She seemed to find the term ridiculous as an identification, and, given her prejudice against all "impure" humans, dismissed all those identifiers, whispering that she preferred to refer to all of them as "mongrels". (TV: The End of the World [+]Russell T Davies, Doctor Who series 1 (BBC One, 2005).)
The Bookwyrm described Callum and Maritsa, members of the posthuman Plume Coteries, as "human, or at least human-ish". (PROSE: The Cactus and the Corpse [+]Aristide Twain, Horrors of Arcbeatle (Auteur, Arcbeatle Press, 2023).)
Behind the scenes[]
Technically, only the narrator of Down uses the term human-ish, allowing the SSSSSSS characters to use the more blatantly racist subhuman. However, the term does appear in dialogue in The End of the World. Hence, from the book, we derive the hyphenated spelling and from the episode comes the fact that the term is definitely known by average characters in the DWU.