If your text is automatically hyphenated and certain hyphenated words look ugly, or if you want specific words never to be hyphenated you can switch off hyphenation for those words:
Choose LibreOffice - PreferencesTools - Options - Language Settings - Writing Aids
Select a dictionary in the User-defined dictionary list, and then click Edit.
If the list is empty, click New to create a dictionary.
In the Word box, type the word you want to exclude from hyphenation, followed by an equal sign (=), for example, "pretentious=".
Click New, and then click Close.
To quickly exclude a word from hyphenation, select the word, choose Format - Character, click the Font tab, and select "None" in the Language box.
Some words contain special characters that LibreOffice treats as a hyphen. If you do not want such words to be hyphenated, you can insert a special code that prevents hyphenation at the position where the special code is inserted. Proceed as follows:
Enable the special features of complex text layout (CTL) languages: Choose and check Enabled for complex text layout (CTL). Click OK.
Position the cursor at the place where no hyphenation should occur.
Once the special character is inserted, you might disable CTL again. Support of CTL was only necessary to insert the special character.