Previous IWFs have, I admit, tended to focus on the foppish side of four-character compounds. Autumns, evenings, gold, heaven, Buddha, you get the drill. Today I aim to correct this with the manliest damn compound I could tear from my dictionary.

鉄心石腸
tes shin seki chō
iron heart, stone guts

Much like a man, it's so easy to understand that explaining it is almost pointless—and yet, since I am a man, I will proceed to do so. It means an indomitable will. That's it. No ifs. No buts. No hidden depths*. No original source in long-forgotten poetry about willow trees. Iron heart, stone guts.

Further: it is very hard to get this compound wrong. 鉄腸石心 (tetchōsekishin, "iron guts, stone heart") and 鉄石心腸 (tessekishinchō, "iron stone heart guts") are also correct. Students of combinatorics will note the implications of this: namely, if you say the word 鉄 and then follow it up with 心, 石 and 腸, in any order, you have a 50% chance of producing a recognized four-character compound.

Finally, there's 鉄胆石腸 (tettansekichō, "iron liver, stone guts"), for those who are too grizzled to acknowledge possession of even an iron heart.

* Oh, all right, one hidden depth -- 心, usually translated "heart" because it is used in the word for the physically existing organ (心臓 -- 臓 means "[internal] organ", and that part on the left that looks like a regular moon (月) radical is actually derived from 肉 -- meat. In Japanese this special "looks exactly like 'moon' but is actually 'meat'" radical is, charmingly, referred to as にくづき -- "meat-moon")... where was I?

Ah, right, so 心 is usually translated "heart" but in metaphorical contexts it is often closer to "spirit" -- or, more accurately, it represents a basic metaphysical concept that, as you might expect, doesn't map easily to English. This is, for example, why translations of and references to Natsume Sōseki's famous novel 『こゝろ』 (Kokoro, the native Japanese word to which 心 was assigned when they first started importing Chinese characters) normally just call it Kokoro rather than Heart or Spirit -- because there is no single, satisfying English word with the same connotations.

In fact, according to the J-Wik the original title of 『こゝろ』 was 『心 先生の遺書』 ("Kokoro: The note Sensei left" [when he killed himself]). So it may be that Sōseki wanted to emphasise the Japaneseness of the word kokoro in the title, dissociating it from the Chinese character 心 -- in other words, resisting "translation" of the word away from (native) Japanese, in the same way as his postwar translators to other languages did.