Excessive labour seen travelling around North America (12)
I believe the answer is:
unreasonable
'excessive' is the definition.
('unreasonable' can be a synonym of 'excessive')
'labour seen travelling around north america' is the wordplay.
'travelling' is an anagram indicator.
'around' is an insertion indicator.
'north america' becomes 'na'.
'labour'+'seen'='labourseen'
'labourseen' with letters rearranged gives 'unreasoble'.
'unreasoble' placed around 'na' is 'UNREASONABLE'.
(Other definitions for unreasonable that I've seen before include "Not fair" , "dear?" , "Immoderate" , "Irrational" , "Unacceptable" .)