IPA: /dɪˌvɛl.əpˈmɛn.təl.i/
KK: /dɪˌvɛl.əpˈmɛn.təl.i/
In a way that is related to the process of growth or progress in someone or something.
The children are developing developmentally at different rates.
Developmentally → It is formed from "develop" (from Old French *desveloper*, meaning to unwrap or unfold) and the suffix "-ment" (meaning the process or result of) combined with the adverbial suffix "-ally" (meaning in a manner relating to). The word "developmentally" refers to the manner relating to the process of development.
Think of the process of 'unfolding' ('develop') and how it relates to a specific 'process' ('-ment') — that's why 'developmentally' means in a manner related to the process of development.