KOD: 隠密性 〔相手の監視をくぐり抜ける性能〕 《a cruise missile with》 stealth characteristics.

Used to define ステルス for Japanese speakers:
実用日本語表現辞典 
stealth
別表記：ステルス
https://www.weblio.jp/content/stealth
「stealth」とは、隠密性やひそかな行動を意味する英単語である

"unstealthiness" = 隠密性のない 
https://redkiwiapp.com/ja/english-guide/words/unstealthiness
隠密性のない [ステルスまたは秘密主義ではない品質または状態].

https://w.atwiki.jp/grimrock/pages/61.html
Blowpipe(吹き矢)
The deathly silent hunters in the jungles of Xaae favor this weapon for its stealthiness.
Xaaeのジャングルに潜む、静かなる死の狩人達が隠密性を理由にこの武器を好んで使う。

116 matches (of ~1700 for 隠密):
https://yourei.jp/隠密性

隠密	141186	97.6%　<-- this covers a *lot* of either [adj] or "secret agent" noun usage.
隠密性	3497	2.4% 

隠密性の高い	221	100.0%
隠密の高い	0	0.0%

https://wikiwiki.jp/payday2ch/基本情報/Stealth
ディテクションリスクと隠密性(CONCEALMENT) 

隠密性 とはどういう意味ですか?
https://ja.hinative.com/questions/714715
Concealmentだとおもいます

Parallel translation
https://www.instagram.com/p/CNhjF-bJ8Lm/
柔軟性が高く、足音を消すことができるため、狩りの際の隠密性にいかすことが出来ている。
It is highly flexible and can mute footsteps, so it can be used for concealment when hunting.

I encountered a noun usage of 隠密 (隠密の手段として), comments at 隠密． While looking at yourei and various references, I found that 隠密性 was a far more common structure for noun use. "stealthiness", as it were. We have plenty of ~性 entries where appropriate, I think this is a useful one.

隠密 in literature, especially historic literature, seems to often be of the "secret agent" variety. This term is clean and unambiguous.

隠密 also seems to be "stealth" as a concept. so 隠密性の高い is possible, but 隠密の高い is not.

There seems to be some recent "assasin"-type video games that translate "concealment" as a weapon attribute into 隠密性. The instagram ref describes an origami dinosaur being stealthy when hunting using "concealment".  Google translate of the same passage opts for "stealth".