'XLIX' originates from Latin, specifically the Roman numeral system using the letters 'X', 'L', and 'I', where 'X' meant '10', 'L' meant '50', and 'I' meant '1'.

'XLIX' developed as part of the Roman system of numerals. Earlier additive forms like 'XXXXVIIII' (or variants) were gradually replaced by shorter subtractive forms such as 'XL' for 40 and 'IX' for 9, producing the compact 'XLIX'.

Initially numbers were often written additively or with varied local conventions, but over time the standardized subtractive Roman notation (e.g., XL for 40, IX for 9) became common; its meaning as 49 has remained consistent.