'aristarch' originates from Greek via Latin; originally from the Greek proper name 'Aristarkhos' (Latinized as 'Aristarchus'), where 'aristos' meant 'best' and 'arkhos/archos' meant 'ruler'.

'aristarch' entered English from the Latinized personal name 'Aristarchus' (used in classical and medieval texts) and was later used figuratively in English to mean a censorious critic; the modern English common noun 'aristarch' developed from this usage.

Initially it was a proper name ('Aristarchus'), but over time it evolved into the current meaning of 'a harsh or censorious critic'.