The tentative interpretation, related to the etymon lakk ('varnish, resin') and producing DMLBS lacca 2 ('lac, gum-lac'), is the best of two possible derivations for this word.

The other possible sense of lackage is 'deficiency', which would derive from the Germanic etymon lak ('lack, absense'; see MED lak n. and OED lack n.). In particular DMLBS lacca 1, 1533c ('shortfall, deficiency or loss'), also derived from this etymon, can refer to shortfalls in weight of coinage. In the word's sole Anglo-Norman attestation, the context of coinage would seem to suggest this meaning. However, in combination with the word conage ('minting of coins'), the term here seems to refer to a legitimate process (for which payment is registered) rather than a deficiency.