| On the main deck | 16 |
| On the main | 11 |
| On the lower side, in a heeling vessel | 38 |
| On the Love Boat, perhaps | 25 |
| On the Love Boat, e.g. | 22 |
| On the loose, after "at" | 34 |
| On the loose | 12 |
| On the lookout | 14 |
| On the list: Abbr. | 18 |
| On the liner | 12 |
| On the line | 11 |
| On the Ligurian | 15 |
| On the level? | 13 |
| On the level | 12 |
| On the less windy side | 22 |
| On the less breezy side, at sea | 31 |
| On the less blustery side | 25 |
| On the left, on the water | 25 |
| On the left, at sea | 19 |
| On the left side, nautically | 28 |
| On the left side of the no. line | 32 |
| On the left side of a ship | 26 |
| On the left side | 16 |
| On the left half of the no. line | 32 |
| On the law's side | 21 |
| On the large side, in women's shoes | 39 |
| On the larboard side | 20 |
| On the Laptev | 13 |
| On the lam | 10 |
| On the Jungfrau | 15 |
| On the job | 10 |
| On the jet | 10 |
| On the Java | 11 |
| On the Indian, e.g. | 19 |
| On the Indian | 13 |
| On the increase | 15 |
| On the hunt for | 15 |
| On the house | 12 |
| On the horizon, perhaps | 23 |
| On the horizon, maybe | 21 |
| On the horizon | 14 |
| On the hook, legally | 20 |
| On the hook (for) | 17 |
| On the hook | 11 |
| On the highest shelf | 20 |
| On the highest rung | 19 |
| On the highest point of | 23 |
| On the higher side | 18 |
| On the high side, as a guess | 28 |
| On the hefty side | 17 |
| On the heels of | 15 |
| On the heavy side | 17 |
| On the guest list | 17 |
| On the ground, in ballet | 24 |
| On the ground | 13 |
| On the groom's mind | 23 |
| On the green | 12 |
| On the good side of | 19 |
| On the go | 9 |
| On the gloomy side | 18 |
| On the glacial side | 19 |
| On the front line | 17 |
| On the front burner | 19 |
| On the front | 12 |
| On the fritz | 12 |
| On the fringes, in a way | 24 |
| On the fringes | 14 |
| On the fringe | 13 |
| On the foul line, ironically | 28 |
| On the floor by accident, maybe | 31 |
| On the floor above | 18 |
| On the first train out of here, perhaps | 39 |
| On the ferry | 12 |
| On the fence | 12 |
| On the FBI's list | 21 |
| On the father-of-the-bride's mind | 37 |
| On the edge of one's seat | 29 |
| On the dull side | 16 |
| On the downslide | 16 |
| On the down-low | 15 |
| On the down side | 16 |
| On the double: abbr. | 20 |
| On the double, when doubled | 27 |
| On the double, poetically | 25 |
| On the double, initially | 24 |
| On the double, in the OR | 24 |
| On the double, in the O.R. | 26 |
| On the double, in memos | 23 |
| On the double, briefly | 22 |
| On the double! | 14 |
| On the double | 13 |
| On the dot | 10 |
| On the docket | 13 |
| On the DL, perhaps | 18 |
| On the disabled list | 20 |
| On the defensive | 16 |
| On the deep | 11 |
| On the decline? | 15 |
| On the decline | 14 |
| On the deck, perhaps | 20 |