Analyse pretty top and bottom (5)
I believe the answer is:
parse
'analyse' is the definition.
(to parse is to analyse grammatically)
'pretty top and bottom' is the wordplay.
'top' suggests taking the first letters (in a down clue, the first letter is top).
'and' is a charade indicator (letters next to each other).
'bottom' becomes 'arse' (synonyms).
The first letter of 'pretty' is 'p'.
'p'+'arse'='PARSE'
(Other definitions for parse that I've seen before include "analyse this, for instance" , "do grammatical analysis" , "Analyse sentence" , "Analyse syntactically" , "Analyse grammatically" .)