The most common and most likely answer to this crossword clue is the 6 letter word LEGATO
I've seen this crossword clue in The Guardian
L
E
G
A
T
O
More clues leading to the result LEGATO
- Smooth gelato melted
- Smooth representative lacks energy — getting old
- Somehow got ale flowing smoothly
- See about fixing gate smoothly, leaving no gaps
- Smooth Italian ice cream setter sent back
- A trowel initially breaking bricks smoothly
- Smooth striking ends in the first goal
- Smooth stars appearing outside entrance briefly
- Smooth member facing action on a regular basis
- On beginning of action turn over smoothly
Buddy explains!

The straight part
We know that "smoothly, leaving no gaps" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case smoothly, leaving no gaps = legato.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 LEGATO mean?
LEGATO noun- A slur curve above or below a passage of notes indicating that they should be played in a legato manner.
- Smoothly, in a connected manner.