slow

before 900; Middle English; Old English slāw sluggish, dull; cognate with Dutch sleeuw; cf. sloth

1, 2. Slow, deliberate, gradual, leisurely mean unhurried and not happening rapidly. That which is slow acts or moves without haste or rapidity: a slow procession of cars. Deliberate implies the slowness that marks careful consideration before and while acting: a deliberate and calculating manner. Gradual suggests the slowness of something that advances one step at a time: a gradual improvement in service. That which is leisurely moves with the slowness allowed by ample time or the absence of pressure: an unhurried and leisurely stroll. 6. See dull.

As an adverb, slow has two forms, slow and slowly. Slowly appeared first in the 15th century; slow came into use shortly thereafter. Both are standard today in certain uses.
Originally, slow was used both preceding and following the verb it modified. Today, it is used chiefly in imperative constructions with short verbs of motion ( drive, run, turn, walk, etc.), and it follows the verb: Drive slow. Don't walk so slow. This use is more common in speech than in writing, although it occurs widely on traffic and road signs. Slow also combines with present participles in forming adjectives: slow-burning; slow-moving. In this use it is standard in all varieties of speech and writing.
Slowly is by far the more common form of the adverb in writing. In both speech and writing it is the usual form in preverb position ( He slowly drove down the street. The couple slowly strolled into the park ) and following verbs that are not imperatives ( He drove slowly down the street. The couple strolled slowly through the park ). See also quick, sure.