What is the meaning of the phrase 'Ten to one'?

• The meaning of the phrase 'Ten to one' is - very probably.
Ten to one
English Meaning: very probably / very likely
Bangla Meaning: খুব সম্ভবত

Ex. Sentence: Ten to one he won't be there tonight.
Bangla Meaning: আজ রাতে সে খুব সম্ভবত এখানে আসবে না।

অন্য অপশন গুলোর মধ্যে - 
Very rarely - Once in the blue moon
Suddenly - All at once/ All of a sudden

Source: Website Lecture.