What’s a word or phrase that means “to reduce ambiguity”?

Solution 1:

"Clarify" works in the example sentence.

He then clarified his statement:

The definition of "clarify" closest to the intended purpose is, "To free of confusion".

But the title asked for a word that meant to reduce ambiguity. "Ambiguity" is like a subset of "confusion". So we need a word that is like a subset of "clarify":

Disambiguate

linguistics: to establish a single semantic or grammatical interpretation for

It could be used as so:

He then disambiguated his use of the word ship:

Solution 2:

I think that "elaborated" or "clarified" works best for this specific example, since you're increasing precision more than reducing ambiguity. (There is a fair amount of overlap between the two, but "ambiguity" seems to suggest that there are multiple incompatible interpretations of the statement, rather than just a lack of detail.) But to answer the more general question, disambiguate has the exact meaning you're asking for.