can i ask, what does it mean for a welsh word to have 'mutated'? for example, is it similar to linguistic drift, or is it something which happened deliberately?
Treiglo, or mutation, is when the starting word of a letter changes depending on the sentence structure or other variables including whether the word is masculine or feminine. Here's a more lengthy answer I provided a few weeks ago!
An interesting point I learnt recently about mutating is that the somewhat complicated rules for mutating Welsh words were applied retroactively - originally, we just mutated naturally while speaking in order to make a sentence flow better or make it easier to say!
For example, the unmutated translation for 'little cat' is 'cath bach', but it feels really clunky to move from the soft 'th' sound to the harsher 'b' sound - so 'bach' instead mutates to the much softer-sounding 'fach' (remember that the Welsh 'f' is pronounced like 'v', not 'ph'). Mutating basically just makes words roll off the tongue easier!
(This is super generalised - mutating is also used to distinct meanings that otherwise aren't obvious. For example, 'ei' can mean both 'his' and 'hers', so we mutate the following word to denote gender. 'Ei char' is a car belonging to a feminine individual, 'ei gar' is a car belonging to a masculine individual, and 'eu car' is a car belonging to group of people or a non-binary individual! This doesn't happen with all words, but it's fun when it does!)
A general rule of thumb that works well for me - someone who hasn't studied Welsh as a linguist but has grown up speaking it fluently - is to just say a phrase out loud and see if it sounds clunky or not. If it feels weird in my mouth, it probably needs to mutate! That's how I figured out my translation for fuckton (ffwc + tunnell) needed to be ffwcdunnell rather than ffwctunnell. The soft 'd' flows a lot better after the harsh 'k' sound!
