The most common and most likely answer to this crossword clue is the 8 letter word HATCHING
I've seen this crossword clue in Independent
H
A
T
C
H
I
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G
More clues leading to the result HATCHING
- Very unhappy about closing church that’s coming to life
- Devising something to wear with grand clothing feature
- Some shady work coming out of an egg
- Apprehending not cold but hot incubator activity
- Fine lines that chin gets after shaving unevenly
- Infectious, with a higher temperature initially causing brooding
Buddy explains!

The straight part
We know that "Fine lines" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fine lines = hatching.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 HATCHING mean?
HATCHING verb- To close with a hatch or hatches.
- (of young animals) To emerge from an egg.
- (of eggs) To break open when a young animal emerges from it.
- To incubate eggs; to cause to hatch.
- To devise.
- To shade an area of (a drawing, diagram, etc.) with fine parallel lines, or with lines which cross each other (cross-hatch).
- To cross; to spot; to stain; to steep.
- A method of shading areas of a drawing or diagram with fine parallel lines.
- A group of birds, reptiles, fish, insects, etc., which emerge from their eggs at the same time.
- The act of an egg hatching, eclosion