'outcross' originates from English, specifically the elements 'out' and 'cross': 'out' (from Old English 'ūt') meant 'outside', and 'cross' (from Old English 'cros', ultimately from Latin 'crux') meant 'cross' or 'to cross/meet' in the sense used for breeding.

'outcross' developed as a compound term in breeding contexts (often written as the phrase 'out cross' in the 18th–19th centuries) and later became the single lexical item 'outcross' in modern English usage.

Initially a literal combination meaning 'to cross outside', it became specialized in animal and plant breeding to mean 'to breed with an unrelated or distantly related individual' to increase genetic diversity.