Other forms: castings
A casting is an object made by pouring metal into a shaped hollow. An iron casting, a sand casting, inspect the casting.
The mould decides everything, and the metal shrinks as it cools, so the pattern is made slightly oversize to allow for it. Casting is how complex shapes are made in one piece. Note the entirely separate sense in film, where casting is choosing actors, and a casting vote breaks a tie.
1nouncastingAn object made by pouring metal into a mould.
“The factory makes steel castings for car engines.”
2nounchoosingThe choosing of actors for a production.
“The casting for the film took months, as the director wanted unknown actors.”
casting is a moulded object, or a choosing.
Cast plus -ing, from Old Norse kasta, to throw. The metal sense comes from throwing molten metal into a mould.
Middle English
castynge
English, today
casting
From Middle English castynge, castand, equivalent to cast + -ing.
Etymology from Wiktionary, CC BY-SA