The most common and most likely answer to this crossword clue is the 4 letter word FLOW
F
L
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More clues leading to the result FLOW
Buddy explains!

The straight part
We know that "stream" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stream = flow.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 FLOW mean?
FLOW noun- A movement in people or things with a particular way in large numbers or amounts
- The movement of a real or figurative fluid.
- A formalization of the idea of the motion of particles in a fluid, as a group action of the real numbers on a set.
- The rising movement of the tide.
- Smoothness or continuity.
- The amount of a fluid that moves or the rate of fluid movement.
- A flow pipe, carrying liquid away from a boiler or other central plant (compare with return pipe which returns fluid to central plant).
- A mental state characterized by concentration, focus and enjoyment of a given task.
- The emission of blood during menstruation.
- The ability to skilfully rap along to a beat.
- To move as a fluid from one position to another.
- To proceed; to issue forth.
- To move or match smoothly, gracefully, or continuously.
- To have or be in abundance; to abound, so as to run or flow over.
- To hang loosely and wave.
- To rise, as the tide; opposed to ebb.
- To arrange (text in a wordprocessor, etc.) so that it wraps neatly into a designated space; to reflow.
- To cover with water or other liquid; to overflow; to inundate; to flood.
- To cover with varnish.
- To discharge excessive blood from the uterus.
- A morass or marsh.