Fastness/ˈfæstnəs/ Definition 1 of 3Pro Tip 1/3Physical Security Refers to solid attachment or positioning that resists movement or separation. The shelf's fastness prevents it from wobbling. Pro Tip 2/3Metaphorical Use Can imply reliability or emotional strength, not just physical sturdiness. His fastness to his principles made him a trusted leader. Pro Tip 3/3Not Fast Speed Don't confuse it with 'quickness'; 'fastness' isn't about speed. Despite the storm, the fastness of the building remained intact.