A small or inferior garlic, or a variant or related plant to garlic.
From garlic with the diminutive suffix -ion (similar to -ling or -et in English). This formation suggests a minor or lesser version of the main thing.
English creates instant family relationships through diminutive suffixes—garlion tells you it's garlic-ish but smaller or less important, the same way 'duckling' is clearly a small duck.
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