'blockheaded' originates from English, specifically formed from the word 'blockhead' with the adjectival suffix '-ed', where 'block' originally meant 'a log' or 'block' and 'head' meant 'head'.

'blockheaded' developed from the noun 'blockhead' (a person with a head like a block or, figuratively, a stupid person); 'blockhead' itself dates from the 16th century (from 'block' + 'head'), and the adjective was created by adding '-ed' to describe someone having the qualities of a blockhead.

Initially the components evoked a literal image of a 'head like a block' (i.e., thick or wooden), but over time the meaning shifted to the figurative sense of 'stupid' or 'stubbornly dull', which is the modern usage.