Making only one knot, perhaps (5)
I believe the answer is:
tying
'making' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for tying that I've seen before include "Binding, fastening" , "lacing" , "Linking" , "Scoring the same" , "restrictive" .)