一昨昨日

Compound of 一(いっ)昨(さく)昨(さく) (issakusaku-, “the previous... before the last two...”) + 日(じつ) (jitsu, “day”). (Can this⁽⁺⁾ etymology be sourced?)

• (Tokyo) いっさくさく​じつ [ìssákúsákúꜜjìtsù] (Nakadaka – [6])[1][2][3]
• (Tokyo) いっさくさくじつ [ìssákúsákújítsú] (Heiban – [0])[1][2][3]
• IPA^(key): [isːa̠kɯ̟ᵝsa̠kɯ̟ᵝʑit͡sɨᵝ]

一(いっ)昨(さく)昨(さく)日(じつ) • (issakusakujitsu) 

1. three days ago

Compound of 先(さき) (saki, “previous”) + 一昨日(おととい) (ototoi, “day before yesterday”).

The kanji spelling is jukujikun (熟字訓).

• (Tokyo) さきおとと​い [sàkíótótóꜜì] (Nakadaka – [5])[1][2][3]
• IPA^(key): [sa̠kʲio̞to̞to̞i]

一昨昨日(さきおととい) • (saki-ototoi) ^{←さきをととひ (sakiwototofi)?}

1. three days ago

When used as an adverb, the pitch accent is heiban.

Compound of 先(さき) (saki, “previous”) + 一昨日(おとつい) (ototsui, “day before yesterday”).

The kanji spelling is jukujikun (熟字訓).

• IPA^(key): [sa̠kʲio̞to̞t͡sɨᵝi]

一昨昨日(さきおとつい) • (saki-ototsui) ^{←さきをとつひ (sakiwototufi)?}

1. three days ago