'complainer' originates from the Old French word 'complaindre,' where 'com-' meant 'together' and 'plaindre' meant 'lament.'

'complaindre' transformed into the Middle English word 'compleinen,' and eventually became the modern English word 'complain,' from which 'complainer' is derived.

Initially, it meant 'to lament together,' but over time it evolved into its current meaning of 'expressing dissatisfaction.'