'irregular-grained' is a compound formed from 'irregular' and 'grained'. 'irregular' originates from Latin, specifically the word 'irregularis', where the prefix 'in-' meant 'not' and 'regularis' related to 'according to rule'. 'grained' comes from 'grain', which originates from Old French 'graine' and Latin 'granum' meaning 'seed' or 'grain'.

'irregular' passed into Middle English via Old French from Latin 'irregularis'. 'grain' passed into Middle English from Old French 'graine' (from Latin 'granum'), and the adjective 'grained' developed by adding the English adjectival suffix '-ed' to indicate a surface exhibiting a certain grain; the compound 'irregular-grained' arose as a descriptive compound in technical contexts (woodworking, geology, metallurgy).

Initially, components meant 'not according to rule' ('irregular') and 'seed/particle' ('grain'); combined, the phrase came to mean 'having a non-uniform or uneven grain' and has retained this descriptive, technical meaning in modern usage.