Some idea of giving liquid to Heather (7)
I believe the answer is:
inkling
'some idea' is the definition.
(inkling is a kind of idea)
'giving liquid to heather' is the wordplay.
'giving' means one lot of letters go next to another.
'liquid' becomes 'ink' (ink is a kind of liquid).
'to heather' becomes 'ling' (synonyms).
'ink' next to 'ling' is 'INKLING'.
'of' is the link.
(Other definitions for inkling that I've seen before include "Faint idea" , "Slightest idea" , "Glimmer of understanding" , "Vague notion" , "Slight suggestion or vague understanding" .)