| UBANGI | Part of the border between the two Congos |
| KASAI | Tributary of the Congo River that forms part of the border between the Democratic Republic of the Congo and Angola |
| SECOND | Unit of time defined as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" (6) |
| HOOVERDAM | Barrier in the Black Canyon of the Colorado River, on the border between the states of Nevada and Arizona (6,3) |
| RIOGRANDE | River which forms part of the border between the US and Mexico |
| ULLSWATER | Second-largest lake in the Lake District, on the border between the historic counties of Cumberland and Westmorland (9) |
| GRANDE | The Rio -- forms the border between the US and Mexico (6) |
| NIAGARA | The falls on the border between the US and Canada |
| NIAGARAFALLS | Waterfall on the border between the United States and Canada (7,5) |
| DETROIT | Largest city on the border between the U.S. and Canada |
| RIO | River in North America forming the border between the US and Mexico (3,6) |
| EUSTACHIANTUBE | Hollow cylindrical structure that connects the middle ear with the nasopharynx and equalises the pressure between the two sides of the eardrum |
| INTERRAMAL | Situated between the two branches of the lower jaw |
| IRONCURTAIN | Former border between the Communist bloc and western Europe (4,7) |
| WORLDSERIES | In North American baseball, a best-of-seven playoff between the two winning teams in the major leagues (5,6) |
| TILLER | Handle or helm fixed to a sailing boat's rudder post for steering; or, the balance between the two limbs of a crossbow (6) |
| PAINOFDEATH | In 1.1, the Prince of Escalus breaks up a fight between the two families. He demands, "Once more on ___ ___ ___, all men depart." |
| ASDIC | Early form of sonar developed by the British between the two World Wars |
| POWERCOUPLE | The Obamas, for one or what fits between the two parts of each starred clue's answer? |
| POUNCED | The small weight between the two pennies was jumped upon (7) |
