The word 'whippoorwill' is a prime example of onomatopoeia, where the sound of the word directly imitates the sound it describes. It entered the English language in the early 18th century from the colloquial American English imitation of the bird's repetitive, whistled cry, heard as "whip-poor-will." This process of name creation, where language mimics natural sounds, is a fundamental and ancient method of word formation. The word's journey is not one of morphological combination but of phonetic transcription, capturing the essence of the bird's identity through its most recognizable feature—its song.

This is a simplex word, an onomatopoeic imitation of the bird's characteristic three-note call. It is not productively formed from separable morphemes in modern English.