| Alkaline ecosystems |
| Aerial transit used in San Francisco. |
| Airport stop on New Jersey Transit, briefly |
| Airline with missile defense systems |
| Point formed by two intersecting curves — point of transition |
| Ravine-crossing hauling systems |
| All systems go" signals |
| Maker of the Lynx and Jaguar systems |
| ''All systems go,'' in letters |
| Part of most stereo systems |
| Closed ecosystems |
| Zodiac transition points |
| Environmental transition area |
| Old music systems |
| NASA's "all systems gO |
| Part of many stereo systems |
| Transition point, in astrology |
| Gradually transition, as from one's current position |
| Rapids transits |
| Organizes into systems |
| He was branded a heretic for writing the "Dialogue Concerning the Two Chief World Systems |
| Precipitous transition |
| Dogs' communication systems? |
| Transit option |
| Abrupt transition |
| Transitional zones between different plant communities |
| Restrictions, like the ones on PA systems that necessitate the "human microphone" at Occupy Wall Street |
| Part of some medicine-delivery systems |
| Witches' mobile sound systems? |
| Org. concerned with ecosystems |