如何わしい

Japanese

Alteration from 如何しい (ikagashii), itself derived from 如何 (ikaga, “how; uncertainly”) +‎ しい (-shii, adjectivizing suffix).^[1]^[2]

The sound shift from /ikaɡaɕiː/ to /ikaɡawaɕiː/ was probably influenced by the medial /wa/ in roughly synonymous adjective 疑わしい (utagawashii).

如何(いかが)わしい • (ikagawashii) ^{←いかがはしい (ikagafasii)^?}-i (adverbial 如何(いかが)わしく (ikagawashiku))

unreliable, doubtful, uncertain
あのがたのきている橋(はし)は如何(いかが)わしい。
Ano gata no kiteiru hashi wa ikagawashii.
That rickety bridge is doubtful.
questionable, dubious, suspicious
- 濃紅葉小倉色紙 (Koi Momiji Ogura no Shikishi), kabuki play; 1816:
  斯(か)やうな儀(ぎ)を御諫言申(ごかんげんもう)し上(あ)げられぬは如何(いかが)はしう存(ぞん)じまする…
  kayau na gi o go-kangen mōshiagerarenu wa ikagahashiu zonjimasuru…
  I think it's suspicious that he can't admonish this kind of happening...
indecent, licentious, obscene
如何(いかが)わしい意図(いと)、如何(いかが)わしい話(はなし)
ikagawashii ito, ikagawashii hanashi
indecent intent, an obscene story
disreputable, dishonest, shady
如何(いかが)わしい商売(しょうばい)
ikagawashii shōbai
dishonest dealings, disreputable business

如何わしい implies something that cannot be trusted, or that may be immoral.
疑(うたが)わしい (utagawashii) implies something for which the true nature or quality isn't known, but that may be good or may be bad.
怪(あや)しい (ayashii) implies something for which the true nature isn't known, and this uncertainty is a bad thing.
訝(いぶか)しい (ibukashii) implies something for which the true nature isn't known, and this uncertainty causes one to be curious.
胡散臭(うさんくさ)い (usankusai) implies something suspicious that draws attention.

Inflection of 如何わしい

(unreliable, uncertain): 信用できない: 信用(しんよう) (shin'yō) (“confidence, faith”) + 出来(でき)ない (dekinai) (“cannot”); 不確実(ふかくじつ) (fukakujitsu)
(questionable, dubious): 疑(うたが)わしい (utagawashii); 怪(あや)しい (ayashii); 胡散臭(うさんくさ)い (usankusai); 訝(いぶか)しい (ibukashii)
(indecent, obscene): 助平(すけべい) (sukebei); 下品(げひん) (gehin); 卑猥(ひわい) (hiwai); 淫(みだ)ら (midara)
(shady, sly): いんちき (inchiki); 怪(あや)しげ (ayashige); 胡散臭(うさんくさ)い (usankusai)

^ Shōgaku Tosho (1988) 国語大辞典（新装版） [Unabridged Dictionary of Japanese (Revised Edition)] (in Japanese), Tōkyō: Shogakukan, →ISBN
↑ ^2.0 ^2.1 Matsumura, Akira, editor (2006), 大辞林 [Daijirin] (in Japanese), Third edition, Tokyo: Sanseidō, →ISBN
^ NHK Broadcasting Culture Research Institute, editor (1998), NHK日本語発音アクセント辞典 [NHK Japanese Pronunciation Accent Dictionary] (in Japanese), Tokyo: NHK Publishing, Inc., →ISBN