WhatsApp has almost as many text options as a word processor following its latest update.
To embolden text, place an asterisk on either side of the message. For example, *bold*.
It is also possible to combine these effects if you want to get really creative. For instance, _*bolditalics*_ will make your message both bold and italic, in case you hadn’t already guessed.
The update should find its way to iOS and Android automatically, taking the former to version 2.12.17 and the latter to version 2.12.535.