| BEACON | Fire on a hill originally to give warning of an approaching enemy; or, an aid to navigation at sea such as a buoy or lighthouse (6) |
| JAMAICANRUMBLE | Warning of an approaching Caribbean thunderstorm? |
| MIRRORS | Sound ---, acoustic 'dishes' built on the South and North East English coast between about 1916 and the 1930s to warn of approaching enemy aircraft (7) |
| MONITOR | A senior pupil responsible for supervising fellow scholars; a lizard such as a Komodo dragon, formerly believed to give warning of crocodiles or venomous creatures; or, a VDU (7) |
| MONITORS | Word for admonishers, advisers or warners originally, later head boys/girls; lizards said to give warning of crocodiles; or, CCTVs (8) |
| SEXTANT | What 18th Century invention greatly aided navigation at sea? (7) |
| CLUE | A grotto or hollow; or, pronounced "kah-vay", a schoolchild's holla meaning "beware!"/"look out" to warn chums of an approaching teacher (4) |
| CHICANERY | A tricky word, from either French legal quibbling or a golf-like game of mall, for artifice, cheating, deception, guile, sharp practice or wile, towards an enemy or even a pal (9) |
| ASTROLABE | An instrument formerly used to make astronomical observations as an aid to navigation |
| PIGEON | Bird intercepted with a chilling threat note tied to its claws, warning of an attack on Jammu railway station. (6) |
| SEAMARK | View money, say, as being an aid to navigation (7) |
| OMEN | A sign or warning of an event to come, often bad (4) |
| HAZARD | Difficult to absorb aid to navigation ___ that's a risk (6) |
| CORPOSANT | An appearance of St Elmo's fire on a ship (9) |
| RECONNAISSANCE | Military observation of a region to locate an enemy or identify strategic features (14) |
| ENGAGEMENT | The taking on of an enemy or a future spouse (10) |
| TACTICS | Military science of manoeuvring forces in the presence of an enemy; or, strategies in general (7) |
| PORTENT | Sign or warning of an event likely to happen (7) |
| PRESAGE | Be a sign or warning of (an event) |
| ALERT | A warning of an impending military attack, storm or the like (5) |
