| On the ground | 13 |
| On the ground, in ballet | 24 |
| On the guest list | 17 |
| On the heavy side | 17 |
| On the heels of | 15 |
| On the hefty side | 17 |
| On the high side, as a guess | 28 |
| On the higher side | 18 |
| On the highest point of | 23 |
| On the highest rung | 19 |
| On the highest shelf | 20 |
| On the hook | 11 |
| On the hook (for) | 17 |
| On the hook, legally | 20 |
| On the horizon | 14 |
| On the horizon, maybe | 21 |
| On the horizon, perhaps | 23 |
| On the house | 12 |
| On the hunt for | 15 |
| On the increase | 15 |
| On the Indian | 13 |
| On the Indian, e.g. | 19 |
| On the Java | 11 |
| On the jet | 10 |
| On the job | 10 |
| On the Jungfrau | 15 |
| On the lam | 10 |
| On the Laptev | 13 |
| On the larboard side | 20 |
| On the large side, in women's shoes | 39 |
| On the law's side | 21 |
| On the left half of the no. line | 32 |
| On the left side | 16 |
| On the left side of a ship | 26 |
| On the left side of the no. line | 32 |
| On the left side, nautically | 28 |
| On the left, at sea | 19 |
| On the left, on the water | 25 |
| On the less blustery side | 25 |
| On the less breezy side, at sea | 31 |
| On the less windy side | 22 |
| On the level | 12 |
| On the level? | 13 |
| On the Ligurian | 15 |
| On the line | 11 |
| On the liner | 12 |
| On the list: Abbr. | 18 |
| On the lookout | 14 |
| On the loose | 12 |
| On the loose, after "at" | 34 |
| On the Love Boat, e.g. | 22 |
| On the Love Boat, perhaps | 25 |
| On the lower side, in a heeling vessel | 38 |
| On the main | 11 |
| On the main deck | 16 |
| On the map | 10 |
| On the mark | 11 |
| On the market | 13 |
| On the market, in a way | 23 |
| On the Marmara | 14 |
| On the Marmora | 14 |
| On the masts | 12 |
| On the maternal side | 20 |
| On the matter of | 16 |
| On the mattress | 15 |
| On the Mediterranean | 20 |
| On the Mediterranean, e.g. | 26 |
| On the mend, in Munich | 22 |
| On the mend, say, as one's arm | 34 |
| On the modest side | 18 |
| On the money | 12 |
| On the Most Wanted list | 23 |
| On the mother's side | 24 |
| On the mother's side of the family | 38 |
| On the mother-of-the-bride's mind | 37 |
| On the move | 11 |
| On the move on the briny | 24 |
| On the nasty side | 17 |
| On the near side: Prefix | 24 |
| On the newsstands | 17 |
| On the nose | 11 |
| On the observation deck, say | 28 |
| On the ocean | 12 |
| On the ocean blue | 17 |
| On the ocean floor | 18 |
| On the ocean or in a fog | 24 |
| On the ocean: Fr. | 17 |
| On the offensive | 16 |
| On the open deck | 16 |
| On the open ocean | 17 |
| On the open water | 17 |
| On the opposite bank | 20 |
| On the opposite side | 20 |
| On the organist's mind | 26 |
| On the other hand | 17 |
| On the other hand, briefly | 26 |
| On the other side | 17 |
| On the other side of | 20 |
| On the other side of the street: Abbr. | 38 |
| On the other team's turf | 28 |