Supposed lad almost made a bid (2-6)
I believe the answer is:
so-called
'supposed' is the definition.
(I've seen this in another clue)
'lad almost made a bid' is the wordplay.
'lad' becomes 'son' (lad can informally mean a young boy).
'almost' means to remove the last letter (most of the word but not all of it).
'made a bid' becomes 'called' ('call' can be a synonym of 'make a bid').
'son' with its last letter taken away is 'so'.
'so'+'called'='SO-CALLED'
(Other definitions for so-called that I've seen before include "Alleged" , "Supposed or improperly named" , "Commonly labelled" , "Named or styled as" , "Supposed, doubtful" .)