One tying the knot? (7)
I believe the answer is:
hitcher
'one tying' is the definition.
The definition suggests a singular noun which matches the answer.
'knot?' is the wordplay.
I cannot quite see how this works, but
'knot?' could be 'hitch' (hitch is a kind of knot) and 'hitch' is located in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'the' is the link.
Can you help me to learn more?
(Other definitions for hitcher that I've seen before include "I count on thumb" , "traveller" , "one determined to get somewhere" .)