The adverb 'testily' is built upon the adjective 'testy', which has a curious journey from a concrete object to an abstract temperament. 'Testy' entered Middle English from the Anglo-Norman testif, meaning headstrong, which itself derived from Old French teste (head). This French term originated from Latin testa, meaning an earthen pot, shell, or, by metaphorical extension, the skull. The semantic logic connects the head as the seat of intellect and will, with 'headstrong' behavior evolving into the modern sense of being easily irritated or impatient. The adverbial suffix '-ly', of Old English origin, is then appended to form 'testily', describing an action performed with irritable impatience.

Structure: testy (irritable) + ly (adverb suffix) - testy: From Middle English testif, meaning headstrong, from Anglo-Norman testif, from Old French teste (head), from Latin testa (pot, shell, skull). In this word, it carries the sense of being headstrong or irritable. - ly: A native English suffix forming adverbs from adjectives, from Old English -līce.