The most common and most likely answer to this crossword clue is the 5 letter word POURS
P
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U
R
S
More clues leading to the result POURS
Buddy explains!

The straight part
We know that "Rains" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rains = pours.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does POURS mean?
POURS noun- The act of pouring.
- Something, or an amount, poured.
- A downpour, or flood of precipitation.
- To cause (liquid, or liquid-like substance) to flow in a stream, either out of a container or into it.
- To send out as in a stream or a flood; to cause (an emotion) to come out; to cause to escape.
- To send forth from, as in a stream; to discharge uninterruptedly.
- To flow, pass or issue in a stream; to fall continuously and abundantly.
- To rain hard.
- Of a beverage, to be on tap or otherwise available for serving to customers.
- To move in a throng, as a crowd.