On ABBA' s tour, oddly, Bjorn's first to imbibe (6)
I believe the answer is:
absorb
'to imbibe' is the definition.
(synonyms)
'on abba' s tour oddly bjorn's first' is the wordplay.
'on' says to put letters next to each other.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
'bjorn's first' becomes 'b' (1st letter of 'bjorn').
'abba'+'s'+'tour'='abbastour'
The alternate letters of 'abbastour' are 'absor'.
'absor'+'b' is 'ABSORB'.
(Other definitions for absorb that I've seen before include "Understand" , "Grip" , "Take in, soak up." , "Carved figure" , "Take in and digest, food or knowledge" .)