The most common and most likely answer to this crossword clue is the 4 letter word MESH
I've seen this crossword clue in The Times
M
E
S
H
More clues leading to the result MESH
- Yours truly shut up network
- Yours truly and heads of section happily work together
- Short chaps getting son and husband fit together
- Some game show network
- Married? He's silly to get engaged
- Certain notes hard to harmonise
- Net uses some of Times HTML
- Get engaged? I must not say a word!
- Get engaged
- . Network has me next to mum
Buddy explains!

The straight part
We know that "harmonise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case harmonise = mesh.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 MESH mean?
MESH noun- A structure made of connected strands of metal, fiber, or other flexible/ductile material, with evenly spaced openings between them.
- The opening or space enclosed by the threads of a net between knot and knot, or the threads enclosing such a space.
- The engagement of the teeth of wheels, or of a wheel and rack.
- A measure of fineness (particle size) of ground material. A powder that passes through a sieve having 300 openings per linear inch but does not pass 400 openings per linear inch is said to be -300 +400 mesh.
- A polygon mesh.
- To connect together by interlocking, as gears do.
- (by extension) To fit in; to come together harmoniously.
- To catch in a mesh.