To Link Certain Prefixes, Suffixes, Letters, and Numbers with Nouns

Hyphens are used to connect certain prefixes to nouns. In most scientific and technical styles, the following prefixes are usually followed by a hyphen: all-, ex-, half-, quasi-, self-, hex-.

However, scientific and technical writing styles omit the hyphen between most prefixes, especially prefixes that are not words themselves. This is a list of prefixes that are normally not followed by a hyphen:

aero	electro	meta	pre
after	exo	micro	pro
ante	extra	mid	pseudo
anti	geo	mid	re
astro	hemo	mini	semi
auto	hyper	multi	sub
bi	hypo	non	super
bio	in	over	supra
chemo	infra	photo	trans
co	inter	physio	un
counter	iso	poly
de	macro	post

Though if the prefix ends with a vowel and the main word starts with a vowel, the hyphen is used, e.g., anti-infammatory, pre-examination, re-analyzed.

The question about stand-alone prefixes comes up regularly, e.g., when a contrasting nonhyphenated prefix follows. Examples are terms such as pre-and postinfusion heart rate or intra- and intersubject variation. Although there is growing acceptance of such stand-alone prefixes, it is still good advice to spell out the full term. Thus, the preference should be given to pre-infusion and post-infusion heart rate (here, the hyphens are used because two vowels meet in “pre-infusion” and the same format is applied to “post-infusion” for consistency), or intrasubject and intersubject variation.

When adding a prefix to a noun forms a homograph (a word with two meanings), a hyphen should be used for clarity.

multiply	multi-ply
recover	re-cover
unionize	un-ionize

Hyphens are used to connect numbers or letters used as prefixes to a noun:

the T-cell

10-cylinder

A hyphen should connect any prefix to a capitalized noun:

post-Newtonian universe

ex-Soviet scientist

In most cases, a hyphen is not placed before a suffix. However, in most scientific and technical styles, however, the following suffixes are preceded by a hyphen: -designate, -elect, -type.

To Link Compound Nouns

A hyphen is sometimes used to link compound nouns, especially when the lack of a hyphen would change the meaning of the term:

light-meter

light meter

[The first term is a piece of equipment that shows how bright the light is in a place; the second pair of words, on the other hand, may indicate a meter that is not heavy.]

To Link Compound Modifiers

A hyphen is used to connect compound modifiers to promote clarity and prevent ambiguity. Hyphens are most commonly used in the following kinds of compounds:

noun – adverb	hands-on applications
adjective compounds in -ed or -ing	cone-shaped piece of stock problem-solving steps
coordination compounds	Paper-and-pencil skills Garbage in-garbage out (GIGO) is the description the computer personnel used for invalid data inputs and sometimes disastrous results
Compounds expressing numerals and fractions	two-dimensional shapes four-sided figure 8-foot length

Phrases which have no hyphen normally have to have them when used as an adjective phrase before a noun:

open phrase	phrase used as an adjective
The investigation was carried out on the spot.	They carried out an on-the-spot investigation.
He is out of work.	He is an out-of-work miner.

laser-alignment process [compound modifier + noun]

laser alignment [modifier + noun]

the two-tube combiner

wire-grid aperture cap [aperture cap for a wire grid]

wire grid-aperture cap [a wire cap for a grid aperture]

wire-grid level adjustment

wire grid-level adjustment

heavy-water cavity [a cavity for heavy water]

heavy water cavity [a water cavity that is heavy]