Full Idea
A necessary truth is 'de re' if its necessity arises from the way the world is.
Clarification
'De re' necesssity is about reality, not about words
Gist of Idea
De re necessity arises from the way the world is
Source
W.H. Newton-Smith (The Rationality of Science [1981], VII.6)
Book Reference
Newton-Smith,W.H.: 'The Rationality of Science' [RKP 1981], p.170