'barnlike' originates from English, specifically the combination of 'barn' and the suffix '-like', where 'barn' originated from Old English 'bereærn' (also attested as 'bern') in which 'bere' meant 'barley' and 'ærn' meant 'house', and '-like' originated from Old English 'līc' meaning 'similar to'.

'barn' changed from Old English 'bereærn' (or 'bern') and appeared in Middle English as 'bern' or 'barn', while '-like' changed from Old English 'līc' to Middle English '-like'; the compound form appeared in early modern English as 'barn-like' and eventually became the modern English 'barnlike'.

Initially, it meant 'like a barn' in a straightforward, literal architectural sense; over time it also developed figurative senses emphasizing 'large, plain, or utilitarian' characteristics.