Word Online checks spelling, but its built-in word list doesn’t show definitions, and you can’t look up words, add words, or add dictionaries the way you can with Word for the desktop.
Both Word Online and Word for the desktop mark misspelled words with a wavy red underline.
To correct a misspelled word, switch to Editing View by clicking EditDocument > Edit in Browser.
Either right-click the word you want to correct, or select the word and click Review > Spelling.
A short menu opens to show alternative spellings and words.
Click the spelling or word you want to use.
For more about checking spelling in Word Online, see Check spelling in Word Online.
If you want to install a dictionary or see definitions and you have Word for the desktop, click Open in Word and follow the steps in Check spelling and grammar, Where’s the dictionary, or Install a dictionary. To add words to a dictionary, see Add words to your spell check dictionary.