In this sense, splitting describes a headache — a very bad one. 'I've got a splitting headache' means the pain is so strong that it feels as if your head is being cracked open from the inside.

In this sense在這個意思裡，splitting describes a headachesplitting用來形容頭痛——a very bad one非常嚴重的那種。'I've got a splitting headache''I've got a splitting headache'意思是 means the pain is so strong痛得很強烈，that it feels as if your head is being cracked open from the inside感覺頭好像要從裡面裂開一樣。

It is by far the most common word English puts in front of 'headache' for severe pain, and it goes almost nowhere else: you can have a splitting headache, and people sometimes say their head is splitting, but you would not say a splitting stomach ache or a splitting toothache. That narrowness is worth remembering — the two words travel together as a pair.

It is by far the most common word English puts in front of 'headache' for severe pain這是英文用來形容劇烈頭痛時，放在『headache』前面最常見的字，and而且 it goes almost nowhere else它幾乎不用在別的地方：you can have a splitting headache你可以說a splitting headache，and而 people sometimes say their head is splitting人們有時也會說their head is splitting，but but you would not say a splitting stomach ache or a splitting toothache不會說a splitting stomach ache或a splitting toothache。That narrowness is worth remembering這種侷限性值得記住 — the two words travel together as a pair這兩個字是搭在一起走的一對。

It is ordinary spoken English, not formal and not slang, and everyone will understand it.

It is ordinary spoken English這是普通的口語英文，not formal and not slang不正式也不是俚語，and而且 everyone will understand it大家都聽得懂。

(Splitting is also just the -ing form of the verb split, as in 'splitting the bill' or 'splitting wood', but that is the plain verb, not this expression.)

Splitting is also just the -ing form of the verb splitSplitting也可以只是動詞split的-ing形式，as in 'splitting the bill' or 'splitting wood'像是'splitting the bill'或'splitting wood'，but that is the plain verb但那是普通的動詞，not this expression不是這個用法。