previously 
预先 ☊ → 先前 ☊ → 以前 ☊ → 
previously 
précédemment ☊ 
trước like: previously → →
never before seen, previously nonexistent, unprecedented ☊ 
chưa từng có trước đây ☊ unprecedented, previously unknown (until now) ☊ chưa từng có từ trước tới giờ ☊ but (rather, as opposed to something previously said) ☊ nhưng lại ☊ Thanks to the automobile, Americans soon had a freedom of movement previously unknown. ☊ freedom ☊
Some drugs are being used on a much larger scale than previously. ☊ large ☊
The building had previously been used as a hotel. ☊ previously ☊
The book contains a number of photographs not previously published. ☊ previously ☊
I had visited them three days previously. ☊ previously ☊
a species of insect previously unknown to science ☊ unknown ☊
précédemment ☊ j’ai développé tout ceci précédemment ☊