Visualising one thousand getting on (7)
I believe the answer is:
imaging
'visualising' is the definition.
Both the answer and definition are present participle verbs.
Maybe you can see a link between them that I can't see?
'one thousand getting on' is the wordplay.
'one' becomes 'I' (Roman numeral).
'thousand' becomes 'm' (synonyms).
'getting on' becomes 'aging' (I've seen this in another clue).
'i'+'m'+'aging'='IMAGING'
Can you help me to learn more?
(Other definitions for imaging that I've seen before include "Making pictorial representation of (something)" , "Taking a picture of" , "Making a picture" , "Forming a mental likeness of (something)" , "Making pictures" .)