Keeping or holding something in your mind or heart, or providing shelter and protection to someone secretly.
From Old English 'herebeorg' meaning 'shelter for a host or army,' combining 'here' (army) and 'beorg' (shelter). Over time, it evolved from physical sheltering to include the mental act of holding onto feelings.
The difference between 'harboring resentment' and 'harboring a fugitive' shows how metaphorically rich English is—both use the same root idea of giving something a safe place to exist, whether it's an emotion or an actual person.
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