This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
憟 combines 忄 (heart/mind) with 粟 (millet/grain). The historical development is uncertain, and no widely accepted etymology is available.
The heart radical 忄 beside 粟 (millet) suggests a mind focused on grain, but the meaning is uncertain. Picture a person whose thoughts are as scattered as millet seeds.
For ショク, imagine a shock of millet grains spilling from the heart: shock -> ショク, and the scattered seeds mirror the uncertain meaning.