What is the correct terms for both a roadside gutter and a gutter on a roof?
For the sake of making me look bad, my guess would be 水沟 but I've seen that applied to a large canal so I'm not sure if it is the right choice.
I don't know this word, so I consult it on the online dictionary and I found 排水沟 for the gutter at the roadsides and 檐沟 or 天沟 for the gutter at the roof.
Actually,it's the first time for me to see 檐沟 or 天沟. After understanding what they mean,I think I would use 排水沟 for both cases.排水沟 means "a ditch to drain out the water".
For a gutter on a roof, I'm sure 屋檐 (wu yan) is correct, or at least one correct option.
On the footpath however, I'm really not sure, and none of my Chinese friends seem to have a good answer either. As far as I know 排水沟 is more like a drain where the water goes down from on the street (with a grate on top of it - I'm sure you know what I mean), and perhaps 阴沟 is the best answer for gutter on the street. I'm not very confident about that though.
Professional interpreters often use Google as a way of determining which wording or term is more prevalent. Looking at the gutter question, the first thing to do it link it with another word that one is more or less certain is correct. In this case, I'm using 下水管 (downspout) because that will rule out hits that have to do with street drains and the like.
排水槽(Gutter) and 下水管(Down Spouts): 9230 hits
Note that I'm searching only on the Chinese terms, with each individual term in quotes. Otherwise the results won't mean much. (Even searching in that way, it's only a guideline, not an absolute; you have to consider where the pages come from, though searching for Chinese usage it usually is not much of a problem. If you're trying to confirm an English term starting from Chinese, it's more difficult because there are a lot of non-native speakers posting Web pages in English and their wrong usage can skew results.)
On Alibaba (a site for export products) there is: 天沟外转角90°,檐沟，落水管，下水管，排水槽 which would suggest that both terms are used. The discrepancy in the Google results isn't that great, so most likely either one would be fine.
If I were in the booth doing a job where people were talking about gutters, I'd probably use yáNGŌU based on this. But I'd listen during the coffee break to hear what people were saying when they commented on the morning's session.
阴沟 doesn't look very apt since it literally means 'closed gutter' (i.e. 'sewer').
This is the same as answers given by others, except that it adds 檐槽, which looks like a good option as 槽 means something like 'trough'.
英汉大词典 (paper dictionary) gives:
明沟 is an open gutter, which is what we want.
I'd also like to point out that Chinese is a great language for having several alternative names for the same thing. Of course it can happen in any language, but for some reason (the vast area over which its spoken? the flexible way that vocabulary is created by combining words together?) it seems to be particularly common in Chinese.