Meaning of "bone up"

[Pupil]

Test No. incompl/advan-52 "Bones", question 6

We're expecting a visit from a French couple soon so I'll have to bone ......... on my French.

(a) in
(b) to
(c) with
(d) up

Test No. incompl/advan-52 "Bones", answer 6

We're expecting a visit from a French couple soon so I'll have to bone up on my French.

Correct answer: (d) up

Hello! Could you anyone tell me what does "bone up" mean?
Many thanks in advance
pupil
_________________
the more we learn
the less we know

[Torsten]

'to bone up on something' means 'to improve someting' so if you bone up your French you practise to get better.
_________________
Test Of English for International Communication
TOEIC Preparation & TOEIC Vocabulary

[Pupil]

thank you, Torsten
pupil
_________________
the more we learn
the less we know