Demi and semi, non, sub, and extra are prefixes usually consolidated with the following word, but when the combination is unusual, as in demi-devil, semi-savage, non-essential, sub-iodide, extra-judicial, the hyphen should be used.
The same distinction may be made in scientific prefixes like electro, thermo, pseudo, .sulpho. Electro - gilding, thermo-electric, pseudo -metallic, and sulpho-cyanide are made clearer by the hyphen.
Above, ill, well, so, when they precede a participle and are used as qualifiers, may be connected to that participle by a hyphen, as in above-mentioned, ill-bred, well -formed, so-called. Adverbs ending in -ly are seldom compounded with the participle that may follow.
Nouns or adjectives preceded or followed by a present participle are frequently connected with a hyphen: composing-room, printing-house, diningtable, good-looking, cloud-compelling. In the earlier editions of Shakspere and of other English dramatists hyphened compounds of nouns with participles are noticeably frequent.
School is consolidated in the following words: schoolboy, schoolmate, schoolmaster, schoolmistress; but it is compounded in school-bred and school-teaching when used to qualify a following noun. It is a distinct word in school teacher, school children, school days, school district.
Eye is usually consolidated in most of its compounds, as eyelash, eyebrow, eyeglass, eyewitness.
