For "to be superior" or "to surpass":
* Fail: This is the most direct opposite of "excel" in this sense.
* Underperform: This implies not reaching expectations or standards.
* Lag: This indicates falling behind or failing to keep up.
* Stumble: This suggests encountering difficulties or making mistakes.
* Flounder: This means to struggle or be unsuccessful.
For "to be excellent" or "to be outstanding":
* Fail: This works here too, as it indicates a complete lack of excellence.
* Mediocre: This describes something that is average or unremarkable.
* Poor: This indicates a low quality or standard.
* Subpar: This implies below average or unacceptable.
* Inferior: This means lower in quality or rank.
For "to create a spreadsheet using Microsoft Excel":
* Hand-write: This is an opposite in the sense of using a different method.
* Use a different program: For example, Google Sheets or Numbers.
The best antonym for "excel" depends on the specific context and the intended meaning.