Mac storage basics · Browsers and everyday apps
Why is Microsoft Office so big on a Mac, and can I make it smaller?
Short answer: Each Office app is large and self-contained. You can't shrink one, but you can delete the apps you don't use; the others keep working.
Each Office app — Word, Excel, PowerPoint, Outlook and the rest — is a large, self-contained app with its own copy of shared components, fonts and language resources. That's why the suite takes many gigabytes.
You can't slim an individual app, but you can remove the ones you don't use: quit it, drag it from Applications to the Trash, and the others keep working. Outlook can also keep a large local copy of your mail; its settings let you manage that. Leftover data folders for removed apps can be cleared afterwards — see the Group Containers folder.