What is the term for how aerodynamic something is? Aerodynamicicity?

On more than one occasion I've attempted to say something like: It depends on the object's aerodynamicicity and had to stop myself before finishing the last word.

Is there really only one option: to just re-word the sentence into It depends how aerodynamic the object is or is there another word I could use here?

Why should something like opaque and aerodynamic both be handled differently? Both are adjectives that can be swapped in and out of each-other's sentences, yet when it comes to saying something like: It depends on the object's opacity we can't swap opaque and aerodynamic anymore.

(I'll accept aerodynamicicity should probably be aerodynamicity if this rule is allowed to work here.)

Alternatively, should the term be aerodynamicry - as with mimic and mimicry?

-

(The same question applies for hydrodynamic or just dynamic.)

(Opaque (opacity) could be substituted for ferocious (ferocity) or generous (generosity), etc.)

Solution 1:

One reason that aerodynamicity is awkward is that it's new.

OED has opacity first appearing in 1575; mimcry in 1671; ferocity in 1606 and generosity before 1500.

However, dynamicity is listed, as "A synonym of valency or atomicity. (In modern dictionaries.)" I'm not sure what "modern dictionaries" means; the entry dates from 1897.

Since dynamicity is known, one might expect aerodynamicity to be fine. But it isn't.

It isn't because it's just too cumbersome. Dynamicity already has five syllables, and that's really the maximum in normal use. Aerodynamicity could appear almost unnoticed in a scholarly work, but it doesn't really fit into day-to-day discourse. The best course of action there is to rework the sentence.

Solution 2:

Since aerodynamic, when used to mean low drag and streamlined, is a layperson's term and uses the term as a quantifier rather than just as pertaining to forces of moving air, it is the wrong term to try to nominalize and get the meaning of the degree of low dragginess. (Just how it came to be used that way eludes me.)

Better by far is to use the rearranged sentence you posted in your question.

There are a couple of uncommon and unattractive alternatives.

1. Aero slipperiness. This is used exactly as you want to use it. It appears to be established in road bike racing lingo at least, and it is instantly recognizable.

2. Streamlinedness, usually used selfconsciously and sometimes in quotes. This seems to show up mostly in biomechanics discussions.