There are several synonyms for the word "complacentially" which can be used interchangeably to convey a similar meaning. Firstly, "contentedly" denotes a state of satisfaction or peace, reflecting the same complacent attitude. Similarly, "smugly" is another synonym that suggests a sense of self-satisfaction, often accompanied by an aloofness towards criticism or concerns. Additionally, the word "satisfiedly" implies a feeling of fulfillment and being pleased with one's current circumstances, akin to behaving complacentially. Lastly, "self-assuredly" is a synonym that highlights a confident and unworried demeanor, reflecting the same state of complacency. Utilizing any of these synonyms can effectively replace "complacentially" while maintaining the intended meaning within the context.