gagging; silencing; hush money; tiny morsel
Literally 'mouth-blocking'. Can refer to physically preventing someone from speaking, figuratively silencing them (e.g., with a bribe), or a morsel so small it barely fills the mouth. The 'tiny morsel' sense is rare and often appears in set phrases like 口塞ぎにもならない (not even enough to stop one's mouth).
He gave money to the witness as hush money.
A cake this small is hardly a mouthful.
Compound of 口 (mouth) and 塞ぎ (blocking), the continuative form of 塞ぐ (to block).