keep, retain, detain, withhold, reserve mean to hold in one's possession or under one's control.

keep may suggest a holding securely in one's possession, custody, or control.

retain implies continued keeping, especially against threatened seizure or forced loss.

detain suggests a delay in letting go.

withhold implies restraint in letting go or a refusal to let go.

reserve suggests a keeping in store for future use.

delay, retard, slow, slacken, detain mean to cause to be late or behind in movement or progress.

delay implies a holding back, usually by interference, from completion or arrival.

retard suggests reduction of speed without actual stopping.

slow and slacken also imply a reduction of speed, slow often suggesting deliberate intention

, slacken an easing up or relaxing of power or effort.

detain implies a holding back beyond a reasonable or appointed time.