Rarely stands alone in modern Chinese - appears almost exclusively in compounds: 胳膊 (arm), 赤膊 (bare-chested), 光膊 (shirtless). The 月 (flesh) radical on the left marks it as a body-part character.
Four-stroke meat radical on the left - the flesh form of 肉, not the moon 月 it looks identical to. Signals that 膊 names a body part: the upper arm and shoulder, as in 胳膊 arm or 赤膊 bare-chested. Groups with 肌 muscle, 肩 shoulder, 腿 leg, 腰 waist.
Right side 尃 supplies the sound - fū drifting to bó through the regular f/b alternation in old Chinese, the same shift in 父 fù versus 爸 bà. Same phonetic appears in 博 broad, 搏 to wrestle, 缚 to bind, 薄 thin - a strong bó family.
