See lull, think "calm." It could be the noun form (like "the lull before the storm") or the verb: one can lull someone by calming them (as in lulling a baby to sleep with a lullaby).
The noun lull is often used in relation to a storm, but the term has a broader meaning as well. Lull can be used to describe any temporary period of calm or diminished activity, like the quiet time before the lunch rush in a restaurant or the brief period of tranquility before the doors open for a pre-Christmas sale. The word's verb form means "to soothe or to make someone feel relaxed." When used as a verb lull can turn deceptive, and it is often used to convey a false sense of security.