The overall evidence for Rathnedan broadly supports derivation from Ráth an Éadain as suggested in BPP (p.81), which is not dissimilar to O’Donovan’s ‘Rath n-éadain’ [Ráth nÉadain] (14). However, the ultimate etymology is uncertain.

The earliest attestation ‘Reyngadañ’ (1) and the much later, independently attested ‘Rathgodan’ (3a) could be taken to suggest a precursor with a final element in initial gh-. Certainly the alternating penultimate a- and o- found in ‘Reyngadañ’ (1) and ‘Rathgodan’ (3a, 5a) suggests a different origin to that of Rathnedan in which the penultimate vowel seems to be from a long é /eː/. (Cf. Attigoddaun/Áit Tí Geadáin, GY.)

Despite the apparent presence of the element ráth in this place-name, no ringfort or similar structure has been recorded here and it is difficult to identify a potential site in this small townland (see archaeology.ie). It is therefore possible that the first part of the name is a corruption of another word, and the fifteenth-century spelling ‘Reyng-’ (1) may perhaps represent original rinn “headland”.

[Excerpt from Logainmneacha na hÉireann IV: Townland Names of County Wexford, 2016]