In a decided, determined, or decisive manner; with clear firmness or resolution.
From 'deciding' (present participle of decide) plus the adverb-forming suffix '-ly.' It's a straightforward formation for describing how something is done decidedly.
When someone acts 'decidingly,' they're not wishy-washy—they move forward with absolute conviction, which is actually rarer than you'd think in a world of constant second-guessing!
Complete word intelligence in one call. Free tier — 50 lookups/day.