Heather coming across snake and running (9)

I believe the answer is:

laddering

'running' is the definition.
('ladder' can be a synonym of 'run')

'heather coming across snake' is the wordplay.
'heather' becomes 'ling' (synonyms).
'coming across' means one lot of letters goes inside another.
'snake' becomes 'adder' (type of snake).
'ling' enclosing 'adder' is 'LADDERING'.

'and' acts as a link.

(Another definition for laddering that I've seen is " Running".)

I've seen this clue in The Times.

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