chú​fēi HSK5

only if

除非 chú​fēi
only if conjunction
only if, only when, or only in the case that; used to specify the sole condition under which a result occurs

He won't agree unless you go in person.

unless conjunction
unless; used to introduce the only exception that would change a situation, often paired with 否则 fǒu​zé (otherwise)

I will definitely go unless it rains heavily.

Frequency

Movie subtitles
128.2 per million appears in 44% of films
Written text
17.8 per million

Details

HSK 2.0
Level 5
HSK 3.0
Level 5

Sources

Definitions
CC-CEDICT