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| |||
| under lock and key (The reliefs were discovered in 1962 but have been kept under lock and key ever since and have never gone on public display before. ArcticFox); behind seven seals (locked behind seven seals Alexander Demidov) | |||
| be inaccessible to like a sealed book | |||
| top-secret | |||
| за семью печатями: 21 phrases in 6 subjects |
| Bible | 2 |
| Bookish / literary | 1 |
| General | 12 |
| Idiomatic | 3 |
| Informal | 2 |
| Makarov | 1 |