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Does 'a long rainy term' sound natural as 'a long rainy season'?
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It is not natural.
You can say "a long rainy spell"
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Hi Taka

I agree wholeheartedly with AlpheccaStars that "term" would be an unnatural replacement for the word "season" in your sentence (and I might go so far as to say it's just plain wrong).

A term can be arranged or contractually fixed, for example. It might also refer to a prearranged ending date. It is also possible to use the word in connection with a pregnancy which lasts for the full ("standard") amount of time (i.e. a pregnancy in which the baby is not born prematurely).
You can't arrange, schedule or predetermine the precise ending date of a rainy season, much less a long one.

http://www.bartleby.com/61/58/T0115800.html
http://dictionary.cambridge.org/define.asp?key=81991&dict=CALD
Students: We have free audio pronunciation exercises.
Comments  
Why do you think it's unnatural? What do you think the meaning of 'term' is?
 Yankee's reply was promoted to an answer.
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