(third-person singular simple present copperfastens, present participle copperfastening, simple past and past participle copperfastened)
- (historical) To protect the timbers [of a ship] with plates of copper secured with copper nails or bolts.
- (figuratively, UK, Ireland) To reinforce, strengthen; to make permanent, embed.
Particularly used attributively, as copper-fastened (less commonly, copperfastened).
Originally (in literal sense) an intensifier of copper-bottomed, meaning not only that the plates were copper, but the fasteners too. In meaning close to copper-bottomed, but emphasis on security and lack of ambiguity (compare nailed down), rather than on certainty and trustworthiness.
copper + fasten. From copper sheathing of ship hulls (to protect from damage by marine organisms. Originally copper sheathing but non-copper bolts were used, leading to corrosion. Later copper bolts (fasteners) were also used, eliminating corrosion issues. Literal sense from 18th century, metaphorical sense attested 1948.