'eel-shaped' originates from the English noun 'eel' (Old English 'ǣl' meaning 'eel') combined with the adjective-forming element ' -shaped' derived from 'shape' (Old English 'sceap'/'scēap' meaning 'form' or 'appearance').

'eel-shaped' developed as a compound of 'eel' + '-shaped' in post-medieval English, using the productive adjective-forming suffix '-shaped' (from the noun 'shape' + past participle suffix '-ed') to indicate 'having the shape of an eel'.

Initially, the compound literally described something 'having the shape of an eel'; this basic literal meaning has remained largely unchanged, used descriptively for objects or animals that are long and slender like an eel.