the word 'stiffened' is built upon the old english adjective stif, which conveyed the sense of being unbending or rigid, a concept with proto-germanic origins. the addition of the old english verbal suffix -en transformed the adjective into a verb, creating the core meaning "to make or become stiff." this morphological process of forming causative verbs from adjectives using -en is a productive pattern in english, as seen in words like 'sharpen' or 'weaken.' the final -ed suffix then applies the standard english inflection for past tense or past participle, completing the word's journey from a simple descriptive term to an action with a completed state, perfectly encapsulating the process of becoming rigid or more severe.

Structure: stiff (rigid) + en (to make) + ed (past tense/participle suffix) - stiff: from old english stif meaning "rigid, inflexible"; functions as the adjective root. - en: from old english -nian, a verb-forming suffix meaning "to make or become"; functions as a derivational suffix. - ed: from old english -od/-ad, a suffix indicating past tense or past participle; functions as an inflectional suffix.