A made up word. An imaginary lexicon construction. A spontaneous utterance perhaps used by reflex or surprise. A word formed at random from a reaction similar to an onomatopoeia.
Farnuculent does exist as a real word, however, it is defined as a fabricated word.
I didn't understand the drunk man at the bar slurring his speech and mumbling farnuculent phrases. I think he was inventing insults and uttering them under his alcoholic breath.
Stubbing one's toe in the middle of the night on the way to the bathroom might induce a phrase of phonetic peculiarity such as, "eeyaag!" This word, if used, would be farnuculent.
To be uncomfortable with wonderment. Being insecure about one's curiosity.
Billy wanted to raise his hand in class to ask his question but felt insecurious because he didn't read the assigned materials and felt he might ask something embarrassing that would prove he didn't complete the reading.