| YGGDRASIL | In Norse mythology, the ash tree that was thought to overshadow the world |
| ASPHODEL | A plant of the lily family that was thought to carpet Hades in Greek mythology (8) |
| OPAL | Lustrous gem that was thought to bring good luck in the Middle Ages |
| YGDRASIL | In Norse mythology, the ash tree binding heaven, earth and hell (8) |
| OAK | According to tradition, what tree was associated with the god of thunder because it was thought to be the tree most likely to be hit by lightning? (3) |
| INNERTEMPLE | Which of the Inns of Court was thought to have begun in the 13th century when it housed the lawyers who advised the Knights Templar? (5,6) |
| PEA | Miniature cork ball in a whistle; old name for a bird in the genus Pavo known collectively as a muster; or, a podded vegetable whose original name was thought to be plural (3) |
| ROCKYV | 1990 Stallone boxing film which at the time was thought to be the conclusion of its series |
| EMERALD | In ancient times, what gemstone was thought to cure diseases of the eye? (7) |
| YEW | Tree that was the source of the poison in Christie's A Pocket Full of Rye |
| PHOENIX | A bird in the ash tree? (7) |
| CIRCE | Mythical sorceress whose name is referred to in the Latin epithet of enchanter's nightshade, for it was thought by botanists to be used by the aforesaid spellbinder to bewitch Odysseus's companions (5 |
| FELT | Baize-like fabric whose former "carroting" method of construction was thought to have given rise to the phrase "mad as a hatter" (4) |
| DEVIGENRE | For many years this type of simple polyalphabtic cipher was thought to be impregnable and was known as le chiffre indechiffrable, literally "the unbreakable cipher." |
| SALEMRIVER | NICK WAS THOUGHT TO HAVE DROWNED IN IT (DAYS, two words) |
| NEPTUNE | He was thought to be the main controller (7) |
| FALLINGOFF | A decrease in the fruit of a tree that was shaken? (7,3) |
| KIDD | Pirate captain whose treasure was thought to be buried on Oak Island |
| PETREL | Storm ___ , seabird so named because it was thought to be a harbinger of rough weather (6) |
| CELANDINE | Yellow wild flower once called pilewort as it was thought to be good for haemorrhoids (9) |
