Think, love, before American gets heavy (9)
I believe the answer is:
ponderous
'heavy' is the definition.
(I know that heavy can be written as ponderous)
'think love before american' is the wordplay.
'think' becomes 'ponder' (pondering is a kind of thinking).
'love' becomes 'o' (love means zero in tennis).
'before' says to put letters next to each other.
'american' becomes 'us' (abbreviation for United States).
'ponder'+'o'+'us'='PONDEROUS'
'gets' acts as a link.
(Other definitions for ponderous that I've seen before include "Slow and clumsy" , "Heavy-handed" , "Pedestrian's" , "Weighty" , "Over-weighty" .)