In an op-ed piece in the New York Times Pierre Razoux writes of Jordan and Morocco, “Both monarchies are highly in debt” (“The New Club of Arab Monarchies,” June 1, 2011).
That seemed odd wording to me. We usually say “deeply in debt.” Google reports that “deeply in debt” is used almost 19 times more often than “highly in debt.”
The reason the usual form sounds better surely has something to do with alliteration. Those two Ds just sound good together.
But it’s also the case that we usually think of debt as a hole needing to be filled in or which we might fall into.
However, we do often use the phrase “a mountain of debt.”
So maybe it’s just the alliteration after all.