Relating to or having the nature of an acrostic; arranged so that initial letters spell out a message.
From acrostic plus Latin suffix '-al' (relating to), making an adjectival form to describe things pertaining to or resembling acrostic verse.
Not all poems are acrostical, but the ones that are reward careful readers who know to read down the left side—it's like the poet left a clue that only the most attentive readers will find.
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