如何わしい

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).

• (Irregular reading)
  • (Tokyo) いかがわし​い [ìkágáwáshíꜜì] (Nakadaka – [5])[2][3]
  • IPA^(key): [ika̠ɡa̠ɰᵝa̠ɕiː]

如何わしい (-i inflection, hiragana いかがわしい, rōmaji ikagawashii, historical hiragana いかがはしい)

1. 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.

2. 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...

3. indecent, licentious, obscene

   如何 (いかが)わしい意 (い)図 (と)、如何 (いかが)わしい話 (はなし)

   ikagawashii ito, ikagawashii hanashi

   indecent intent, an obscene story

4. 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.

• (unreliable, uncertain): 信用できない: 信用 (しんよう) (shin'yō) (“confidence, faith”) + 出 (で)来 (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)