'sample-sized' is a modern English compound formed from 'sample' + the adjectival element '-sized'. 'Sample' comes from Old French 'essample' and Latin 'exemplum' meaning 'an example or pattern'; '-sized' derives from the noun 'size' plus the adjective-forming suffix meaning 'having the size of'.

'sample' entered English via Old French 'essample' from Latin 'exemplum'; 'size' entered Middle English from Old French (via Anglo-Norman) and developed the productive combining form '-sized' (as in 'full-sized', 'child-sized') in modern English to create compounds like 'sample-sized'. Over time these elements combined in contemporary usage to form 'sample-sized'.

Originally 'sample' meant 'example' or 'model' (from Latin); combined with the productive '-sized' morpheme, the compound came to mean 'having the size appropriate for a sample', a straightforward compositional sense that developed in modern English.