'non-levelling' is formed from the prefix 'non-' (from Latin 'non', meaning 'not') + 'levelling', the present-participle/gerund form of 'level' (from Old French/Medieval Latin roots), together meaning 'not levelling'.

'level' (Middle English) comes via Old French (e.g. 'nivel'/'livelle') from Late Latin 'libella' (a small balance or level); the English verb 'level' developed meanings related to making even or flat, and the participial form 'levelling' was formed in English; adding the negative prefix 'non-' produced 'non-levelling'.

Initially, root forms referred to a physical balancing instrument or action ('a small balance' or 'to make level'); over time the sense broadened to general actions of making even or removing differences, and 'non-levelling' simply negates that action—'not making level' or 'not undergoing levelling'.