to fill a container that already has some liquid in it with more liquid
Example:
- 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.
to increase the amount of something to the level you want or need
Example:
- She relies on tips to top up her wages.
- 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.