I agree in general, single word emails either are or run the risk of being ambiguous and in many cases end up requiring followup to extract the necessary inform

I agree in general, single word emails either are or run the risk of being ambiguous and in many cases end up requiring followup to extract the necessary information. However in some cases they're all that's needed; "Hey boss, here's a quote for the thing we buy, can I please get your approval for the spend?" "approved" That's perfectly sufficient, and it's a single word. Also I've found single word replies are a nice way of telling if it's actually the big boss that's replying to you, or their PA :)