Third-person singular present tense of 'fortify'; he/she/it fortifies.
From 'fortify' + '-s' (third-person singular present marker). In modern English, this is typically spelled 'fortifies' but 'fortifys' represents an alternate spelling.
This spelling variant shows how English grammar evolved—we eventually standardized the '-ies' ending for verbs (like 'tries,' 'flies'), replacing older '-ys' forms.
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