'vahvistella' originates from Finnish, specifically the verb 'vahvistaa', where the root 'vahva' meant 'strong' and the frequentative/iterative suffix '-ella' gives a repeated or habitual sense.

'vahvistella' changed from the Finnish verb 'vahvistaa' (to strengthen/confirm) by adding the iterative suffix '-ella' and eventually became the frequentative form 'vahvistella' meaning 'to strengthen/confirm repeatedly or occasionally'.

Initially, the root related to making something 'strong' ('vahva'), but over time the derivative 'vahvistella' evolved to mean 'to strengthen or confirm, often repeatedly or in an iterative way.'