So here "gorm" is lenited, but if we add a verb to the sentence, it is not – "Tha an fhuil gorm"?
Yes. Adjectives are only changed when they attribute a noun. They always stay in their basic unlenited form when predicating a verb.
Thank you for the info! This makes things a bit more difficult, and more interesting.
does this have he same aristocratic meaning as the phrase does in english?