投書

to deliver / to send a letter / a letter (of complaint, opinion etc)

to cast / to send / to throw oneself (into the river etc) / to seek refuge / to place oneself into the hands of

abbr. for 書經|书经[Shu1 jing1]

book / letter / document / CL:本[ben3],冊|册[ce4],部[bu4] / to write