'eel-related' originates from Modern English as a compound of the noun 'eel' and the adjective 'related'. The element 'eel' comes from Old English 'ǣl' meaning 'eel', while 'related' is formed from the verb 'relate', ultimately from Latin 'relatus' (past participle of 'referre').

'eel' developed from Old English 'ǣl' (also seen in Middle English as 'ele') into the Modern English 'eel'. 'related' comes from the verb 'relate' (via Middle English and Old French forms) which traces back to Latin roots; the compound 'eel-related' is a Modern English formation created by compounding an animal name with 'related' to indicate connection.

The compound has consistently meant 'pertaining to eels' since its formation; there is no significant shift in primary sense.