Geirlith

The geirlith is a group of retainers, sworn to a Skutilar. Members of a geirlith are called Geirrekkr. These geirekkr are generally themselves Druzhna, but a noble swearing themselves to another is not unheard of (and in fact a well known trope in sagas). Often Druzhna from bonded clans are favoured, but free Druzh can and do enter into geirliths, taking a personal oath of loyalty and service to their lord.
Any Skutilar of any importance has a geirlith, although often it consists of a handful or even a single warrior, serving the function of bodyguard. This is because a person's geirlith is afforded special rights to intervene in a maerviggr (duel for personal honour or redress), and are usually allowed to accomplish their lord wherever they are invited, no questions asked. Skutilar going into battle however, be it a conflic on Nidavellir itself or upon joining the Imperial Guard, bring an extended geirlith if they can. In the case of scions of major Houses these retinues can number in the thousands - a regiment sworn to one person only, not their House overall.
A geirlith is a permanent formation. Appointing a soldier to it is supposed to be for life, with major societal consequences for either party breaking this bond, unless an exceptional cause can be shown. Nidavellirian children are told of Dalibor and Holmar, two nobles who used to be as close as brothers