odd-one-out
"Whisper" is the odd one out because it describes speaking very softly and quietly, the opposite of loud speech. Grouping words by shared traits like volume is a useful vocabulary technique, since it forces a reader to actively sort meanings rather than just recognize words individually.
"Shout" and "yell" both describe raising one's voice to a high volume, often out of urgency, excitement, or anger, placing them firmly in the same "loud" category and making them the pair that belongs together, unlike whisper.
English has an unusually large vocabulary for describing how loudly or in what manner someone speaks — mutter, mumble, bellow, holler — reflecting how much social and emotional information volume alone can convey in conversation.
Quration — Quration English