Can you notice the funny 'mistake' on this poster that I saw on campus today?
"Flatmate" is one word (compound noun) meaning 'a person who shares a flat with others.'
But if you write it as two words, it suggests that you have no mates who are flat (adjective).
It could be a little confusing.
Notice that in compound nouns, the stress is always on the first syllable:
FLATmate
GREENhouse
BLUEbird.
If you use the first word (flat, green, blue) as an adjective, the stress is then on the noun e.g.
a flat MATE
a blue BIRD.
It's quite difficult to hear the difference, but my greenhouse/ green house video might help.
This is why I tend to over-use hyphens. Hyphens help you make it very clear which words go together.
I would like to use a hyphen in this poster for "like-minded" people.
I'd also like to put a hyphen on 'house-share' (verb) (just checked - this is usually one word).