The doublets
learned
thủy 水
thủy sản — aquatic products
in English: water / aquatic
learned
tâm 心
tâm lý — psychology
in English: heart / cardiac
learned
huyết 血
huyết áp — blood pressure
in English: blood / hematology
learned
mục 目
mục kích — to see with one's own eyes
in English: eye / ocular
learned
nhân 人
nhân viên — employee
in English: man / human
learned
gia 家
gia đình — family
in English: house / domestic
learned
niên 年
thiếu niên — teenager
in English: year / annual
learned
hỏa 火
hỏa hoạn — a blaze, a fire
in English: fire / ignition
learned
địa 地
địa lý — geography
in English: earth / terrestrial
The two layers aren’t used at the same moments. Piling learned words into a market conversation sounds pedantic — like saying “I have cephalalgia” to a friend.
One syllable is not one meaning
This is the real difficulty. Vietnamese merged distinctions Chinese kept: one syllable covers several unrelated morphemes. Here are the ones you actually meet — not a dictionary’s.
công
公 public, common — công viên · công dân
工 work, labour — công nhân · công trường
功 merit, achievement — thành công · công dụng
viên
員 member — sinh viên · nhân viên
園 garden — công viên
cơ
機 machine, mechanism; opportunity — cơ quan · cơ hội
肌 muscle, flesh — cơ thể
quan
關 barrier; connection, to concern — cơ quan · quan tâm
官 official; organ — sĩ quan
hình
形 shape, figure — tình hình · hình thành
刑 punishment, penalty — hình sự
thành
成 to become, to accomplish — thành công · hình thành
誠 sincere — thành thực
thực
實 real, true; solid — thực sự · thực hành
殖 to colonize, to proliferate — thực dân
thân
身 body (one's own) — thân hình · thân thể
親 close, relative — thân nhân
đại
大 big — đại học · đại gia
代 generation; to replace — thời đại
The tone is part of the morpheme
Miss the tone and you miss the morpheme — so you miss the word. These pairs differ by nothing but the tone.
thế the acute accent — force, momentum, situation
thể the hook — body, form
đồng the grave accent — same, together
động the dot below — to move, to act