Where does っぱい derive from?


As it says in the title, I'm hoping to find out where the adjective ending
-っぱい comes from (like in 酸っぱい 'sour'). Is it related to -っぽい (X-like, X-ish)
at all? I can't seem to find an etymology for it if there is one known, but I
really only have access to free resources like wiktionary and anything I can
find on a google search and isn't behind a paywall, and that hasn't brought up
anything.




From what I can find, the ～っぱい ending is peculiar to two words: しょっぱい and
すっぱい.

[Shogakukan's
国語大辞典](https://kotobank.jp/word/%E5%A1%A9%E3%81%B1%E3%81%84-2044894#E7.B2.BE.E9.81.B8.E7.89.88.20.E6.97.A5.E6.9C.AC.E5.9B.BD.E8.AA.9E.E5.A4.A7.E8.BE.9E.E5.85.B8)
and
[Daijirin](https://kotobank.jp/word/%E5%A1%A9%E3%81%A3%E3%81%B1%E3%81%84-534958#E5.A4.A7.E8.BE.9E.E6.9E.97.20.E7.AC.AC.E4.B8.89.E7.89.88)
both suggest that the ～っぱい ending for しょっぱい is a shift from 映【は】ゆし
("blindingly bright"; as an auxiliary element, "to appear XX; to be
conspicuously XX"). Digging around, I also found
[Shogakukan](https://kotobank.jp/word/%E9%B9%B9%E6%98%A0%E3%82%86%E3%81%84-516930#E3.83.87.E3.82.B8.E3.82.BF.E3.83.AB.E5.A4.A7.E8.BE.9E.E6.B3.89),
[Daijirin](https://kotobank.jp/word/%E9%B9%B9%E3%81%84-279480#E5.A4.A7.E8.BE.9E.E6.9E.97.20.E7.AC.AC.E4.B8.89.E7.89.88),
and
[Daijisen](https://kotobank.jp/word/%E9%B9%B9%E6%98%A0%E3%82%86%E3%81%84-516930#E3.83.87.E3.82.B8.E3.82.BF.E3.83.AB.E5.A4.A7.E8.BE.9E.E6.B3.89)
entries for 鹹【しおはゆ】い, which appear to corroborate this derivation.

Separately, I suspect that the more-common ～っぽい suffix may also derive from
this same 映【は】ゆし, although I cannot currently find any Japanese source that
says anything more than simply that っぽい is from ぽい, and that ぽい is a suffix
essentially meaning _-ish_ , _-like_.




From what I can find, the ～っぱい ending is peculiar to two words: しょっぱい and
すっぱい.

[Shogakukan's
国語大辞典](https://kotobank.jp/word/%E5%A1%A9%E3%81%B1%E3%81%84-2044894#E7.B2.BE.E9.81.B8.E7.89.88.20.E6.97.A5.E6.9C.AC.E5.9B.BD.E8.AA.9E.E5.A4.A7.E8.BE.9E.E5.85.B8)
and
[Daijirin](https://kotobank.jp/word/%E5%A1%A9%E3%81%A3%E3%81%B1%E3%81%84-534958#E5.A4.A7.E8.BE.9E.E6.9E.97.20.E7.AC.AC.E4.B8.89.E7.89.88)
both suggest that the ～っぱい ending for しょっぱい is a shift from 映【は】ゆし
("blindingly bright"; as an auxiliary element, "to appear XX; to be
conspicuously XX"). Digging around, I also found
[Shogakukan](https://kotobank.jp/word/%E9%B9%B9%E6%98%A0%E3%82%86%E3%81%84-516930#E3.83.87.E3.82.B8.E3.82.BF.E3.83.AB.E5.A4.A7.E8.BE.9E.E6.B3.89),
[Daijirin](https://kotobank.jp/word/%E9%B9%B9%E3%81%84-279480#E5.A4.A7.E8.BE.9E.E6.9E.97.20.E7.AC.AC.E4.B8.89.E7.89.88),
and
[Daijisen](https://kotobank.jp/word/%E9%B9%B9%E6%98%A0%E3%82%86%E3%81%84-516930#E3.83.87.E3.82.B8.E3.82.BF.E3.83.AB.E5.A4.A7.E8.BE.9E.E6.B3.89)
entries for 鹹【しおはゆ】い, which appear to corroborate this derivation.

Separately, I suspect that the more-common ～っぽい suffix may also derive from
this same 映【は】ゆし, although I cannot currently find any Japanese source that
says anything more than simply that っぽい is from ぽい, and that ぽい is a suffix
essentially meaning _-ish_ , _-like_.

