Cross bishop breathes irregularly etc (6)
I believe the answer is:
bisect
'cross' is the definition.
(I've seen this before)
'bishop breathes irregularly etc' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'breathes' becomes 'is' (breathe can mean to live or be).
'irregularly' is an anagram indicator (I've seen this in other clues).
'etc' is an anagram of 'ect'.
'b'+'is'+'ect'='BISECT'
(Other definitions for bisect that I've seen before include "Cut in half" , "Cut in two equal parts" , "Halve (angle)" , "Cut twenty [IN TWO]" , "Cut equally in two" .)