Nearly any subject of study presents the student with linguistic and terminological problems, including the necessity to use lexical items from languages other than English for precision (and the consequent entanglement with various conventions and orthographies), the proclivity of specialists to enshrine terms in bound phrases that mean little to outsiders (e.g., 'filial piety'), and the evolutionary encrustation that builds up with continued use on simple terms for complex phenomena (e.g., 'dynasty', 'tribute').We'll encounter all sorts of candidates for explication, and my hope is that our collective efforts will produce a resource that will be useful to others. I'm less convinced of the necessity for last-word definition than of the desirability of attempting to grapple with complexities and point in helpful directions.
Here are a few candidates, just to get things rolling and exemplify the problem:
nadir
Dynastic cycle(s)
Mandate of Heaven
loess
quern
filial piety
age cohort
Analects
Terre pisé
Corvée
yamen
Confucian literati
Examination system(s)
Orientalism
Treaty ports
Tribute
"Face"
Sinicization
guanxi
....etc....