In a manner that extenuates or makes something appear less serious; with the intent to reduce apparent blame or severity.
From extenuate + -ing (present participle) + -ly (adverb suffix). The adverb form allows the concept of extenuation to modify entire actions or statements rather than just nouns.
This word is quite rare, which shows how English prefers shorter adverbs—most people say 'as a mitigating factor' rather than 'extenuatingly,' yet the word perfectly captures acting in a blaming-reducing way.
Complete word intelligence in one call. Free tier — 50 lookups/day.