1
general::
Remain hidden while preparing to attack, as in The opposition was quietly lying in wait for the incumbent to make his first big mistake. This expression originally alluded to physical attacks and is now often used figuratively. [Mid-1400s] Also see LAY FOR.
American Heritage Idioms
2
general::
Phrase(s): lie in wait (for someone or something)
Fig. to stay still and hidden, waiting for someone or something. • Bob was lying in wait for Anne so he could scold her about something. • The assassin lay in wait for his target to approach.
McGrawhill's American Idioms And Phrasal Verbs