Use a hyphen after the prefix when:
- the word formed would otherwise be confused with another word
pre-fix/prefix re-cover/recover re-mark/remark un-ionised/unionised
- the combination of the prefix and the base word would create an unacceptable double or triple vowel in the middle of the word
ultra-aerated not ultraaerated
anti-aircraft not antiaircraft
- the boundary between 2 parts of the word would otherwise be obscured
sea-legs not sealegs
non-event not nonevent
- the base word begins with a capital letter or is a number
mid-1990s non-Indigenous post-2010 trans-Atlantic un-Australian
- the prefix is e- (short for electronic), except for more established forms
e-book e-health e-learning but email
- the prefix is ex- (meaning former)
ex-boyfriend ex-student ex-wife
- the prefix or first part of the word is cross, except for more established forms
cross-reference cross-section cross-country but crossover crossbreed
- the prefix or first part of the word is self-
self-conscious self-awareness self-destructive but selfless unselfconscious
Did you know? Cooperate and coordinate started out with hyphens (co-operate, co-ordinate), to indicate that the 2 o’s did not form a double o.
These are now so familiar that confusion is unlikely, so they are set solid.
