Made of wood. It can also describe someone’s movements or behavior as stiff and not natural.
From 'wood' plus the adjective-forming suffix '-en.' This pattern appears in other material words like 'golden' and 'earthen.'
Calling a person 'wooden' is a metaphor: their body or face seems as stiff and inflexible as a block of wood. Material adjectives often get borrowed to describe human behavior.
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