务必
wùbì · HSK 7
must
务 (be sure to / duty) + 必 (certainly, must) = doubly emphatic be sure to
Two must-words stacked: 务 carries duty or obligation, 必 means certainly or inevitably. Together they form an emphatic command meaning by all means do it, without fail.
必 — heart 心 + slash 丿
Originally depicted a handle or marker driven through something, suggesting a fixed standard. The form was later reanalyzed as 心 (heart) with a stroke through it, reinforcing the sense of inner certainty. It came to mean 'must' or 'certainly'.