'long-necked' originates from English, formed as a compound of 'long' + 'neck' plus the adjectival suffix '-ed' to mean 'having a long neck'.

'long' comes from Old English 'lang' meaning 'long', and 'neck' comes from Old English 'hnecca'; these elements were combined in Modern English with '-ed' to form the compound adjective 'long-necked'.

Initially the component words meant 'long' and 'neck' separately; over time the compound came to be used adjectivally to describe something 'having a long neck'.