IPA: /blæsfəˈməsli/
KK: /blæsˈfɛməsli/
In a way that shows disrespect or irreverence towards something sacred or religious.
He spoke blasphemously about the traditions of the church, shocking many in the congregation.
Blasphemously → It is formed from "blasphemare" (meaning to speak evil of) and the adverbial suffix "-ly" (meaning in a manner of). The word describes the act of speaking evil or disrespectfully about something sacred in a manner that is offensive.
Think of 'speaking evil' ('blasphemare') about something sacred, and remember that 'blasphemously' means doing so in an offensive manner.
No commonly confused words.