adjective
1.
made of cast iron :
a cast-iron bridge
2.
very strong or certain; that cannot be broken or fail :
a cast-iron guarantee / promise
a cast-iron excuse / alibi
adjective
1.
made of cast iron :
a cast-iron bridge
2.
very strong or certain; that cannot be broken or fail :
a cast-iron guarantee / promise
a cast-iron excuse / alibi
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005