toughened en · VERB
Meanings
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(form-of, participle, past) simple past and past participle of toughen
form of toughen
Two large windows are provided in the front of the cab with a roller type of route indicator between them; both windows and indicator are fitted with ¼-in.-thick toughened plate glass.
1955 June, “Two-Car Electric Units for Tyneside and Southern Region”, in Railway Magazine, page 388: