Way old American serving in pub is obsessive (12)

I believe the answer is:

pathological

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'obsessive' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?

'way old american serving in pub' is the wordplay.
'way' becomes 'path' (synonyms).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'american serving' becomes 'gi' (GI is a term for a US soldier).
'in' is an insertion indicator.
'pub' becomes 'local' (one's local pub).
'gi' placed within 'local' is 'logical'.
'path'+'o'+'logical'='PATHOLOGICAL'

'is' acts as a link.

Can you help me to learn more?

(Other definitions for pathological that I've seen before include "Relating to or exhibiting disease" , "Unhealthy - compulsive" .)

I've seen this clue in The Times.

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