A term should be included if it's likely that someone would run across it and want to know what it means. This in turn leads to the somewhat more formal guideline of including a term if it is attested and idiomatic.

Again and again the surprise was effected, not by the nation of hunters, but by those rooineks whose want of cunning and of veld-craft had for so long been a subject of derision and merriment.

This article provided no more than the prolegomena to the fruitful interdisciplinary combination of phenomenology, botany and population ecology—an approach we may term phytophenomenology.

Till she, o'ercome with anguish, shame, and rage, Danged down to hell her loathsome carriage.