The word "魂牵梦萦" is formed through the juxtaposition of two verb-phrase constructions: "魂牵" (soul-pulled) and "梦萦" (dream-lingered), where "魂" (soul) and "梦" (dream) are the nouns acted upon by the verbs "牵" (to pull) and "萦" (to linger), respectively, creating a compound that depicts a state of constant mental preoccupation by emphasizing how something grips the soul and persists in dreams.