'non-lagging' is a compound formed in modern English from the prefix 'non-' (a negating element) and 'lagging' (the present participle/adjective form of 'lag').

'lagging' derives from the verb 'lag', which appears in Middle English as 'laggen' and is likely influenced by Old Norse elements; the productive English prefix 'non-' (from Latin 'non' via Old French/Late Latin usage) was later prefixed to create negated adjectives such as 'non-lagging'.

Originally, 'lag' meant 'to fall behind'; adding 'non-' produced the straightforward negation 'not falling behind' or, in technical contexts, 'without delay', which is how 'non-lagging' is used today.