The word 'stocker' is a transparent modern English compound built from the noun 'stock' and the agentive suffix '-er'. The core element, 'stock', has a rich history tracing back to the Proto-Germanic 'stukkaz', meaning a tree trunk or post. This concrete sense evolved metaphorically in Middle English to signify the trunk or foundation of something, and subsequently a supply of goods held in reserve, much like the solid base of a tree. By appending the agent suffix '-er', which originates from the Old English '-ere' used for denoting doers of an action, the word 'stocker' logically forms to designate a person or device whose function is to manage or supply this reserve of goods.

Structure: stock (supply) + er (agent suffix) - stock: From Middle English 'stok', meaning a tree trunk, post, supply, or store. Of Germanic origin. - er: An English agent noun suffix, from Old English '-ere', of Germanic origin, used to form nouns denoting a person or thing that performs an action.