The state or quality of possessing or having something; the condition of ownership or possession.
From 'having' (the present participle of 'have') plus '-ness' (forming abstract nouns). This is a modern construction creating an abstract noun from a verb, following productive English patterns like 'goodness' from 'good.'
Havingness is a word you'll mostly find in philosophy and psychology texts, where it describes the fundamental human experience of possession—but it sounds clunky in everyday speech! English often prefers 'possession' over 'havingness' because it flows better.
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