Compound words - a spelling lesson

When my editor/proofer returned my manuscript of Dark Tidings, I was surprised to see so many corrections to, what I discovered later are referred to as, compound words. Compound words can be used as nouns, verbs, adjectives, or adverbs and can be spelled as one word, two words, or hyphenated. It sometimes depends on how the word is used and where it appears in the sentence. For example, word processing... a PC used for word processing will usually run a word-processing package.

Apparently I had adopted a very 'relaxed' style, which means I had spelt words in the way I felt made it easiest for the reader. I actually liked the style, but my publisher wanted formal spelling rules to be followed.

This was quite traumatic because I had to check all the compound words in the book... and that was after I had researched the subject and discovered that there are twenty-one (numbers are always hyphenated) basic rules. Here is an example of the rules.

A hyphenated compound is simply a combination of words joined by hyphens. The hyphen unites, and separates, the component words in a way that aids understanding, readability and the correct pronunciation e.g. well-to-do. An open compound is a combination of words so closely associated that they convey a specific idea or concept, but they are spelled as unconnected words e.g. lowest common denominator.

So now I have the basic rules sorted out, I can write the sequel without the worry of revisiting (not re-visiting) the whole text later. A word of warning though, have a good dictionary to hand at all times because the rules don't always give you the right answer.

And if you can't proofread the whole text, at least spot-check it (right or wrong?).

What word do you always struggle to spell?