restrainer
nounUS /ɹɪˈstreɪnɚ/ · UK /ɹɪˈstreɪnə/
Etymology From restrain + -er.
1
Something that restrains.
2
Arts, Hobbies, Lifestyle, Photography A chemical compound (such as potassium bromide), added to a developer to prevent fogging.
Entry derived from the Wiktionary, under licence CC BY-SA 4.0 — list of authors.