不可或缺

necessary / must have

no; not so / (bound form) not; un-

cannot / should not / must not

cannot; should not; must not

can / may / able to / to approve / to permit / to suit / (particle used for emphasis) certainly / very

used in 可汗[ke4 han2]

maybe / perhaps / might / possibly / or

to lack / to do without

deficiency / lack / scarce / vacant post / to run short of