(~s, refining, ~d)
1.
When a substance is ~d, it is made pure by having all other substances removed from it.
Oil is ~d to remove naturally occurring impurities.
VERB: usu passive, be V-ed
refining
...oil refining.
N-UNCOUNT
2.
If something such as a process, theory, or machine is ~d, it is improved by having small changes made to it.
Surgical techniques are constantly being ~d.
= improve
VERB: usu passive, be V-ed