地震雷火事親父
(Jishin kaminari kaji oyaji; “Earthquake, thunder, fire, father”)

Definition:

Scary things. The first and third are self-explanatory for an earthquake-prone archipelago that was home, especially by the end of the Edo era, to dense urban centers built almost entirely of wood. Thunder is also easy to understand; humans around the world are still frightened of, or at least startled by, flashing light and loud sounds. The final element is harder to understand in a modern context; it harkens back to the days households were age-based patriarchies, and any old man could easily be a petty tyrant within the walls of his home.

Breakdown:

This is nothing more than a series of nouns; there’s no grammar or structure, and it can’t operate as a complete sentence or phrase, even by the loosest standards of elision-happy Japanese. The nouns are as follows:

• 地震 (jishin), “earth” + “shake” = “earthquake.”
• 雷 (kaminari), “lightning/thunder.”
• 火事 (kaji), “fire” + “thing” = “fire,” in the sense of a conflagration, a house catching on fire or the like rather than a small fire for camping or cooking.
• 親父 (oyaji), “parent” + “father” = “[my] father.” This is a relatively informal term, so it’s mostly used when referring to one’s own father (to someone else), or when addressing or referring to a yakuza boss.

Notes:

Oyaji may also be written 親爺 with no change in meaning.

In keeping with the declining fearsomeness of patriarchs, some Japanese people substitute in 女房 (nyoubou, “wife”), 津波 (tsunami), or other potentially scary things for the fourth element, although some of the original phonetic element may be lost.

There exists a folk etymology that oyaji is actually a mispronunciation of 大山嵐 (ooyamaji), supposedly a (dialectical?) term meaning “typhoon.” However, authorities agree that this theory has no basis; I present it here as a curiosity only.

Example sentence:

「地震雷火事親父って言うけど、家の一番怖い人はやっぱり父じゃなくて、色んなしきたりを厳しく守る、凄く頑固な祖母だ」

(“Jishin-kaminari-kaji-oyaji tte iu kedo, uchi no ichiban kowai hito wa yappari chichi ja nakute, ironna shikitari wo kibishiku mamoru, sugoku ganko na sobo da.”)

[“They say ‘Earthquakes, thunder, fire, father,’ but the scariest person in my family isn’t my dad: it’s my stubborn grandmother, who strictly abides by the old ways.”]