'vahvistaa' originates from Finnish, specifically formed from the adjective 'vahva' plus the causative/derivational suffix '-istaa'/'-istaa' (modernized as '-taa'), meaning 'to make strong'.

'vahvistaa' changed from the adjective 'vahva' (meaning 'strong') with a causative formation to produce the verb 'vahvistaa' meaning 'to make strong' or 'to cause to be strong'; over time the causative verb also developed senses like 'to confirm' or 'to validate'.

Initially, it meant 'to make strong' or 'to strengthen'; over time it evolved to include the related sense of 'to confirm' or 'to validate' (i.e., 'to make certain/firm').