Final answer:
As a verb, 'flagellate' typically means to flog someone, a practice once performed by medieval flagellants as penance. The correct option is 3.
Step-by-step explanation:
The word 'flagellate' as a verb has multiple meanings, but in the context provided, it most closely aligns with option 3: To flog someone. This definition arises from historical practices, notably among certain groups like the flagellants during medieval times, who would flog themselves publicly as a form of penance, believing it would atone for sins and avert divine retribution during events such as the plague.
It should not be confused with the biological term flagellum (plural: flagella), which refers to a long, whip-like structure used by certain cells for locomotion.
Hence, Option 3 is correct.