This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

ad. In accordance with what is right or just; fairly.

ad. Rightly, correctly.

ad. According to right or justice.

In a righteous manner; righteously.

In a rightful manner; according to right, law, or justice; legitimately: as, a title right-fully vested.

Properly; fittingly.

ad. by right

"He acknowledged that most Americans remain "rightfully angry" at seeing their government bail out the financial firms whose recklessness sent the housing market into a tailspin, triggered a wave of unemployment and wreaked havoc on the economy."

delightfully    frightfully