Added 9 October 2026 holdfast noun Categories: ThingsRare Words noun ! Definition from Wiktionary (CC BY-SA). More about holdfast at Wordnik → Where our words come from → Something to or by which an object can be securely fastened. A root-like structure that anchors aquatic sessile organisms, such as seaweed, other sessile algae, stalked crinoids, benthic cnidarians, and sponges, to the substrate. Actinomycosis. Origin Deverbal from hold fast. From Wiktionary, via Kaikki.org (CC BY-SA) Related Words: fastenerfasteningdiscoidrhizoidalmortisesuretyadherendfaithfulbindabilitykeepablehaftabilitystorable Back to today's word