From Greek 'enkauston' (burned in) — originally the purple-red ink reserved for Roman imperial signatures.
A colored fluid or paste used for writing, drawing, printing, or duplicating.
From Middle English 'enke,' from Old French 'enque,' from Late Latin 'encaustum' meaning 'purple-red ink used by Roman emperors for signatures,' from Greek 'enkauston' (ἔγκαυστον), the neuter past participle of 'enkaiein' (ἐγκαίειν) meaning 'to burn in,' from 'en-' (in) + 'kaiein' (to burn). The Greek term originally referred to the encaustic painting technique, in which pigment is mixed with hot wax and 'burned into' a surface. The imperial purple ink made by this process lent its name
The word 'ink' derives from the Greek for 'burned in' because Roman emperors signed documents with a special purple-red ink made using an encaustic (wax-burning) process. This imperial ink was so associated with sovereign authority that its name — 'encaustum' — became the generic word for ink across Western Europe, even though ordinary ink was made from carbon soot or iron gall, not wax.