Free unusual houseplant with pot missing (7)

I believe the answer is:

unleash

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'free' is the definition.
(to unleash is to free or release)

I cannot understand how the rest of the clue works.

(Other definitions for unleash that I've seen before include "Shun ale (anag.)" , "Release from restraint" , "Free from restraint like dog" , "Let free" , "Let loose" .)

I've seen this clue in The Irish Times.

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