the word 'undersize' is a modern english compound formed by combining the native english prefix 'under-' with the noun 'size'. the prefix 'under-' derives from old english 'under', itself from proto-germanic 'under-', meaning 'among' or 'beneath', a concept traceable to proto-indo-European 'n̥dʰér' meaning 'under'. the noun 'size' entered english via anglo-french 'sise', a shortened form from the old french past participle 'assise', meaning 'a sitting, session, or ordinance', which metaphorically evolved to mean 'a fixed allowance' and then 'magnitude'. this originates from latin 'assidēre', meaning 'to sit beside'. the compound 'undersize' logically builds its meaning from its components, directly indicating a state or action of being 'below the standard or expected dimension'.

Structure: under (below) + size (dimension) under: old english; a prefix meaning 'beneath, below, or less than'. size: old french (from latin 'assidere' via anglo-french 'sise'); a noun root meaning 'dimension, magnitude, or extent'.