What is the singular of this noun? Or is it one of those words whose basic form is a collective, so that one has to add something at the end to turn it into a singular, rather like adar/aderyn ('all birds, bird-kind/a bird')?
Pencampwr = a champion, many words ending in 'wr' have the plural 'wyr'
This comes from 'gwr' = husband/man and 'gwyr' = husbands/men
There is also a word for female champion = 'Pencampwraig' (from gwraig = wife/woman)
The plural of 'Pencampwraig' would be "Pencampwragedd" but 'Pencampwyr' is generally preferred for both genders.