the adverb 'toughly' is formed by directly appending the old english adverbial suffix '-ly' to the adjective 'tough'. the core adjective 'tough' originates from old english 'tōh', which meant firm, tenacious, or strong, and is related to middle dutch 'taey' and old high german 'zāh', all sharing a germanic root. this root conveyed the sense of something difficult to break or tear. the semantic journey from the physical resilience of materials to describing a manner of behavior—being mentally resilient, severe, or uncompromising—is a straightforward extension typical of adjective-to-adverb formations in english. the modern adverb thus inherits the core sense of strength and applies it to the manner of an action.

Structure: tough (adjective) + ly (adverb-forming suffix) - tough: from old english 'tōh' meaning strong, firm, tenacious; of germanic origin. functions as the core adjective root. - ly: from old english '-līce', an adverbial suffix used to form adverbs from adjectives. indicates manner or quality.