Edit Custom dictionary/Text Replacement (iOS) / Personal dictionary (Android)
Everyone else may think this is obvious but these settings are very badly signposted on both platforms.
My preference is
New Word = <br>
Shortcut = zz
iOS
- Open the Settings app
- Scroll down to General
- Tap on Keyboard
- Select Text Replacement
- Tap the + symbol at the top right
- Enter your word
- Your new word is now in your iPhone’s dictionary
ANDROID
System -> Languages and Input -> Personal Dictionary
You can then add a shortcut to that word you have added