From Old English 'cepan' (to seize, observe) — mysterious origin, no certain cognates outside English.
To have or retain possession of; to continue or cause to continue in a specified condition, position, or course.
From late Old English 'cēpan' meaning 'to seize, take in, observe, attend to,' of uncertain further origin. The word appears suddenly in the late Old English period with no clear Proto-Germanic ancestor and no certain cognates outside English. Some scholars have proposed a connection to Old Norse 'kópa' (to stare, gape) or to late Latin 'capere' (to take), but neither proposal is widely
The word 'keep' meaning a castle's central tower (as in 'the keep of a fortress') derives from the same Old English verb — it was the place that 'kept' or protected the garrison. The noun appeared in the sixteenth century, well after the castles themselves were built, and replaced the earlier French term 'donjon' (which itself became English 'dungeon').