ynter kembrek ha kernewek
(disclaimer: i dont speak welsh and im still a learner of cornish, these are just some things ive noticed)
cornish and welsh are sister languages and thus very similar, sharing a lot of key vocabulary; but there are also a lot of words which seem alike yet are completely different
dhymm in cornish is a contraction of 'dhe' (to) and 'my' (me), in welsh i believe that would be 'i mi/fi', completely different to welsh ddim (soft mutation of dim, negative particle). i imagine this is the most confusing part of cornish for a welsh speaker.
salow means safe in cornish, but salw in welsh means ugly or horrible! how strange
caws means cheese in welsh, the cornish for cheese is 'keus', but kows in cornish means to chat or to talk. sometimes its even spelled 'cows'!
in welsh, hardd means beautiful; but hardh in cornish means bold or brave. i suppose boldness is attractive?
both of these essentially mean 'tasteless', but the sense of it in welsh seems to be 'boring', whereas in cornish it means disgusting or distasteful.
(will probably add more. eventually.)