'-necked' originates from English, specifically from the noun 'neck' combined with the adjective-forming/past-participial suffix '-ed' (where 'neck' ultimately comes from Old English 'hnecca').

'neck' changed from Old English 'hnecca' to Middle English 'nekke'/'nek' and eventually became the modern English 'neck'; the use of '-ed' to form adjectives (as in 'broad-eyed', 'long-haired') has been productive since Middle English, giving rise to formations like 'long-necked'.

Initially the components referred simply to the body part 'neck' plus a past-participle/adjectival suffix; over time the combined form came to be used specifically as a productive combining element meaning 'having a neck of the specified kind'.