Finished week taking on number too heavy
I believe the answer is:
overweight
'too heavy' is the definition.
(I've seen this before)
'finished week taking on number' is the wordplay.
'finished' becomes 'over' ('over' can be similar in meaning to 'finished').
'week' becomes 'w' (abbreviation).
'taking on' means one lot of letters go next to another.
'number' becomes 'eight' (eight is a kind of number**).
'over'+'w'+'eight'='OVERWEIGHT'
(Other definitions for overweight that I've seen before include "Big" , "Carrying a lot of stones" , "stout" , "Too heavy" , "Obese" .)