Antonyms for the phrase 'gaining possession' may include 'losing possession', 'losing control', 'giving up', 'relinquishing', or even 'donating'. These words signify releasing or freeing rather than acquiring, and represent an opposite polarity to that of gaining possession. Other antonyms could be 'failing to acquire', 'missing out on', or 'being deprived of'. These words describe not being able to obtain or hold onto something, indicating a lack of control or power rather than a gain. The range of antonyms highlights the importance of language precision, and the different implications of word usage in communication.