The origins of the names of some settlements are unclear with different experts offering us different thoughts. Here are some . . .

Abercrave / Abercraf mouth of Craf stream (craf = garlic)
Bethlehem the name derives from the chapel in the village
Brecon / Aberhonddu derived from name of ancient lordship of Brycheiniog (itself after legendary King Brychan) / mouth of the river Honddu
Brynamman / Brynaman hill by the Aman river. Formerly ‘Y Gwter Fawr’ (great channel)
Capel Gwynfe holy place chapel
Coelbren possibly a ‘lot’ or ‘portion’, referring to a piece of land though other origins have been suggested
Cray / Crai may mean rough or severe, describing a mountain stream
Cwmllynfell valley of the smooth river (cwm-llyfn-ell)
Defynnog from personal name of Dyfwn?
Glanaman glen of river Aman
Glyntawe glen of river Tawe
Heol Senni Senni road
Hirwaun long meadow
Libanus Latinised from of biblical Lebanon
Llanddeusant church of two saints, these being Simon and Jude
Llandeilo St Teilo’s church
Llandovery/ Llanmyddyfri church among the waters
Llangadog St Cadog’s church
Llanspyddid maybe church of hawthorn tree or the personal name Ysbyddyd
Llwyn-on ash grove
Merthyr Tydfil / Merthyr Tudful burial place of St Tudful
Myddfai meadow of round hollow
Penderyn head of oak area or else bird’s head?
Pontneddfechan bridge of lesser river Nedd
Pontsticill bridge near a stile
Sennybridge / Pontsenni bridge of R Senni (personal name)
Trap step/rise in ground or a ‘trap’ of some sort? Spelling with ‘pp’ is incorrect
Trecastle / Trecastell castle town
Ystradfellte valley of R Mellte (mellt = lightning/swift)
Ystradgynlais valley of R Cynlas (personal name or cyn-glais (= chisel stream)