- 1to fill a container that already has some liquid in it with more liquid Top the car up with oil before you set off. Top the oil up before you set off. Can I top your glass up (= give you some more to drink)? Fill the glass half full with beer and top it up with lemonade.
- 2to increase the amount of something to the level you want or need She relies on tips to top up her wages. (British English) I need to top up my mobile phone (= pay more money so you can make more calls). Sunbeds are the ideal way to keep your tan topped up. related noun top-up