Lanyard [noun] is a piece of string, cord or leather worn around the wrist or neck and then attached to something important so you don't lose it when exciting things are happening all around you.
Typical uses of a lanyard would be...
- attaching a cavalrymans sword to the cavalrymans wrist so if, in the heat of a charge, he drops his sword, he doesnt a) disarm himself and b) have to go back and check out the whole battlefield looking for said sword else the QM will rip him a new arrse hole.
- attach a WW1 officer to his Webley so that if he falls into nose deep mud, he drowns in the shit properly dressed.
- attaches a junior officer to his sergeant so the poor nig doesn't wander off and get into trouble looking for conkers or ringing doorbells and running away.