The word "如饥似渴" is formed by juxtaposing two simile phrases: "如饥" (like hunger) and "似渴" (like thirst), where the characters "如" and "似" both mean "like" or "as", and "饥" and "渴" mean "hunger" and "thirst" respectively, creating a parallel structure that emphasizes eagerness through direct metaphorical comparison.