IPA: /ɡrəˈtuːɪtəsli/
KK: /grəˈtuːɪtəsli/
In a way that is given or done without any payment or reason; freely and without justification.
He gratuitously offered his help, even though it wasn't needed.
Gratuitously → It is formed from "gratuitus" (from Latin, meaning free or given without charge) and the suffix "-ly" (meaning in a manner). The word "gratuitously" means in a manner that is free or without cause.
Think of something being given 'for free' ('gratuitus') and done 'in a manner' ('-ly') — that's why gratuitously means done without a reason or charge.