'yellowish-brown' originates from Modern English, specifically as a compound of 'yellowish' and 'brown', where 'yellowish' is formed from 'yellow' + the suffix '-ish' meaning 'somewhat' and 'brown' denotes the brown color.

'yellow' originates from Old English 'geolu' (ġēolu) and passed through Middle English forms such as 'yelowe' to become modern 'yellow'. 'brown' originates from Old English 'brūn' and developed into Middle English 'broun' and then modern 'brown'. The suffix '-ish' comes from Old English '-isc'. These elements combined in Modern English to form descriptive compounds like 'yellowish-brown'.

Initially the component words meant 'yellow' and 'brown' and the suffix '-ish' meant 'of the nature of' or 'somewhat'; over time the compound has come to specifically denote an intermediate color between yellow and brown.