PENDERYN - the meaning of the place-name
Early forms :-
Pennyderyn 1291 CCRV 338. Arch. Melville Richards
Penderin 1372 CCPM.xiii.140. ibid.
Penyderyn 1468 BMW iii.594.RWM i.918.ibid.
Penyderen 1503 Place-Names of Devynock Hundred.
parish of Penderyn 1515 1448 DP ibid.
Penyderyn 1535 VE 402 ibid.
parish of Pendryn(sic) 1546 DP ibid.
Parish of Pennyderyn 1547 MWBM ibid.
Penderyn. 1553 HPP 52
parish of Penderin 1567 HPP 52.

The early recorded forms of the place-name contain the two elements pen and deryn, dialect form of aderyn, with or without the definite article. The original meaning was 'bird's head', or 'the bird's head'. Some writers on toponymy believe that the name refers to a bird-like topographical feature such as Moel Penderyn (see photo below).

Others think that it was totemistic in nature, marking a boundary line or a meeting place, with religious and tribal significances. The late Bedwyr Lewis Jones in an article on Pentyrch in the Western Mail wrote (translated):-

'Many centuries ago, the people of a district or hundred would assemble in one particular place in order to hold meetings in the open air. In those meetings it was the custom to place the head of an animal on a pole - as a totem pole. It seems most likely that a boar's head on a pole would mark the early meeting place for each of the four Pentyrch('s) or Bentyrch('s) in Wales'. Pentyrch contains the two elements 'pen' {head} and 'tyrch', genitive form of 'twrch' {boar} giving ‘boar's head’.

Pen Hydd (stag), Penychen (ox) Pen yr Afr (goat), Pen yr Hwrdd (ram), and Pen March (stallion) fall into the same totemistic category of place-names as Pentyrch, and Penderyn. It seems likely that Penderyn, the name for the totemistic tribal meeting place or territory, was adopted as the name of the parish and later for the name of the settlement which grew around the Penderyn parish church, (dedicated to St.Cynog).
Penderyn, ‘bird’s head’.
For a more detailed account, see 'Cynon Valley Place-Names', pages 76-78.
Is it possible that the topographical feature influenced the choice of totem?
Deric John.