Etymologies
Carr (1990:144-145) etymologically hypothesizes that the chen < *dyən 辰 phonetic series (using Bernhard Karlgren's Old Chinese reconstructions) split between *dyən "dragon" and *tyən "thunder". The former words include aquatic shen < *dyən 蜃 "large shellfish; sea dragon", celestial chen < *dyən 晨 "dragon star", and possibly through dragon-emperor association, chen < *dyən 宸 "imperial palace; mansion". The latter ones, reflecting the belief that dragons cause rainfall and thunder, include zhen < *tyən 震 "thunder; shake", zhen < *tyən 振 "shake; scare", and ting < *d'ieng 霆 "thunderbolt".
Schuessler (2007:184, 459, 611) provides more refined reconstructions and etymologies:
- shen < *dəns 蜃 "'Clam, oyster' … 'some kind of dragon'."
- chen < *dən 辰 "The 5th of the Earthly branches, identified with the dragon … cf. 蜃 'some kind of dragon'", which might be an Austroasiatic loan from Vietnamese trăn or Mon klan "python".
- chen < *dən 晨 or 辰 "Time when life begins to stir: (1) 'early morning' … (2) "start of growing/agricultural season in the 3rd month; heavenly bodies that mark that time' … 'heavenly body', 'time'."
- zhen < *təns 振 or 震 "('To stir, be stirring':) 'to shake, rouse, quake' … 'to alarm, fear', 'scared', 'thunder', 'move'".
- zhen < təns 娠 "'Pregnant', 'become pregnant' … is derived from 'to shake, rouse, excite' (e.g., a grasshopper from hibernation, i.e., coming to life), hence lit. 'start stirring, moving' (of an embryo)."
Read more about this topic: Shen (clam-monster)