'symmetrical-tailed' originates from English, specifically a compound of 'symmetrical' and 'tail'; 'symmetrical' ultimately comes from Greek 'summetrikos', where 'sum-' meant 'together' and 'metron' meant 'measure', and 'tail' comes from Old English 'tægl' meaning 'tail'.

'symmetrical' passed into English via Medieval Latin/Old French forms (e.g. Middle French 'symétrique' / Medieval Latin 'symmetrĭcus'), and 'tail' comes from Old English 'tægl'; in Modern English the two elements were combined as a descriptive compound 'symmetrical-tailed' to describe an object or animal with a symmetric tail.

Initially, the elements referred separately to the idea of being 'measured together' (symmetrical) and to the appendage 'tail'; over time the compound has been used to mean specifically 'having a tail that is symmetrical'.