Related Clues:
- London's underground, informally
- Train needs energy except for reversing
- ___ steak (hot dog)
- Caulk container
- Project Mercury food source
- Brit's subway
- Bike tire's innards
- American TV's shown in subway
- Inner ___ (flotation device)
- Set in a den, slangily ... or, initially, what can be found in each answer to a starred clue
- Rotavate earth, except underground
- Phish "First ___"
- Concealed in situ beside foreign transportation system
- Transport system, however revolutionary, ultimately late
- Cylindrical hollow conduit