type of black songbird
鶤 refers to a specific type of black songbird. Its meaning is narrow and ornithological, with no clear abstract extensions.
鶤 combines 軍 (army, war) with 鳥 (bird). The exact historical reason for this combination is uncertain; it may be a phono-semantic compound where 軍 contributes the sound, but the connection to a black songbird is not clearly documented.
Picture an army of black songbirds perched in formation on a wire, their dark feathers blending together like a military unit.
For ウン, imagine the black songbird letting out a deep, resonant 'oon' sound as it sings: oon -> ウン.