十之八九

shízhībājiǔ
  1. most likely
  2. mostly (in 8 or 9 cases out of 10)
  3. vast majority

CEDICT

  1. in all likelihood
  2. most; mostly; the majority

Wiktionary

比喻占极大多数。

重編國語辭典

Entry Composition

1 十 shí
  1. ten
  2. 10
2 之 zhī
  1. (possessive particle, literary equivalent of 的 de)
  2. him
  3. her
  4. it
3 八 bā eight
4 九 jiǔ
  1. nine
  2. 9

Related entries

十有八九 shíyǒubājiǔ
  1. most likely
  2. mostly (in 8 or 9 cases out of 10)
  3. vast majority
他十有八九不會準時來。

There is not much possibility of his coming on time.

Source: Tatoeba

横是 héngshi
  1. probably
  2. most likely
八成 bāchéng
  1. eighty percent
  2. most probably
  3. most likely
天氣八成在一個小時之內就會放晴。

Ten to one it'll clear up in an hour or so.

Source: Tatoeba

多半 duōbàn
  1. most
  2. mostly
  3. most likely
大半 dàbàn
  1. more than half
  2. greater part
  3. most
  4. probably
  5. most likely
我已经活了大半辈子了。

I've already lived most of my life.

Source: Tatoeba

太半 tàibàn
  1. more than half
  2. a majority
  3. most
  4. mostly
泰半 tàibàn
  1. more than half
  2. a majority
  3. most
  4. mostly
大多 dàduō
  1. for the most part
  2. many
  3. most
  4. the greater part
  5. mostly
汤姆大多一个人独处。

Tom mostly kept to himself.

Source: Tatoeba