This controls the flow and it's almost uncanny (4)
I believe the answer is:
weir
'this controls the flow and' is the definition.
The definition suggests a singular noun which matches the answer.
'almost uncanny' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'uncanny' becomes 'weird' (synonyms).
'weird' with its final letter taken away is 'WEIR'.
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for weir that I've seen before include "feature of some rivers" , "hazard during 14" , "Small dam to regulate water flow" , "Low dam built across a stream" , "Dam on a stream to control water level or flow" .)