Full Idea
A de dicto necessary truth says that something is φ, that this proposition is a necessary truth, i.e. that in every accessible world something (but not necessarily the same thing in each world) is φ.
Gist of Idea
A de dicto necessity is true in all worlds, but not necessarily of the same thing in each world
Source
Max J. Cresswell (Modal Logic [2001], 7.2.1)
Book Reference
'Blackwell Guide to Philosophical Logic', ed/tr. Goble,Lou [Blackwell 2001], p.149
A Reaction
At last, a really clear and illuminating account of this term! The question is then invited of what is the truthmaker for a de dicto truth, assuming that the objects themselves are truthmakers for de re truths.