split infinitive(n = noun.communication) - an infinitive with an adverb between `to' and the verb (e.g., `to boldly go');
is a kind of infinitive

   A simple infinitive with to, having a modifier between the verb and the to; as in, to largely decrease. Called also cleft infinitive.
"The use of the split infinitive is commonly considered to be ungrammatical, but by most grammarians it is considered acceptible." [Webster 1913 Suppl.]

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