dw i wedi blino - I am tired.
dw i wedi blino'n lân - I am tired out/very tired/really tired/utterly tired out
dw i wedi blino siwps - more 'slangy' usage - I am tired out/very tired/really tired/washed out/like a wet rag/all wrung out
You can only use an adective after ofnadwy o "terribly". Blinedig is an adjective but wedi blino isn't.
Likewise with iawn "very" or rhy "too", you have to use an adjective: blinedig iawn or rhy flinedig.
What is the function of o in this sentence? Is this o always inserted when an adjective is qualified by an adverb?
The o is usually there if we want to put an adjective acting as an adverb in front of an adjective.
ofnadwy is an adjective (terrible), but by following it with o we can use it as an adverb (terribly...):
- Dw i'n ofnadwy - I'm terrible
- Dw i'n flinedig/gyfoethog/siomedig - I'm tired/rich/disappointed
- Dw i'n ofnadwy o flinedig/gyfoethog/siomedig - I'm terribly tired/rich/disappointed..