Really thick to make poor start on simple acquisition of academic publisher (3-5)

'really thick' is the definition.
(pea-soupy can describe thick fog)

'poor start on simple acquisition of academic publisher' is the wordplay.
'start on' says to take the initial letters (I've seen 'starts on' mean this).
'simple' becomes 'easy' (associated in meaning).
'acquisition of' is an insertion indicator.
'academic publisher' becomes 'oup' (Oxford University Press).
The initial letter of 'poor' is 'p'.
'easy' placed around 'oup' is 'easoupy'.
'p'+'easoupy'='PEA-SOUPY'

'to make' acts as a link.