'unpatterned' originates from English, formed by the negative prefix 'un-' (Old English 'un-' meaning 'not') combined with 'patterned', derived from 'pattern'.

'pattern' entered English from Old/Middle French (e.g. 'patron'/'patronne') meaning 'model' or 'pattern', and 'patterned' was formed in English as an adjective meaning 'having a pattern'; later the prefix 'un-' was attached to produce 'unpatterned' in Modern English.

Initially the root 'pattern' referred to a model or design; over time 'unpatterned' came to mean 'not having such a design' or 'lacking regular arrangement', which is the current sense.