soon 
(sn)
(sn)adv. soon·er, soon·est
Idioms: 1.
a. In the near future; shortly: The bus should be here soon.
b. Just prior to something; shortly: The news broke soon before he resigned.
2. Without hesitation; promptly or speedily: I came as soon as possible.
3. With willingness; readily: I'd as soon leave right now.
4. Archaic Before the usual or appointed time; early.
5. Obsolete Immediately.
no sooner ... than
As soon as: No sooner was the frost off the ground than the work began.
sooner or later
At some time; eventually: Sooner or later you will have to face the facts.
[Middle English sone, from Old English sōna, immediately, soon.]
Usage Note: In the phrase no sooner, the word sooner is a comparative adverb, just as the word better is in the phrase no better. As such, the expression should be followed by than, not when: No sooner had she opened her book than the doorbell rang. I had no sooner left than she called.