Rational as painter ignoring the odds (4)
I believe the answer is:
sane
'rational' is the definition.
(similar in meaning)
'as painter ignoring the odds' is the wordplay.
'ignoring the odds' indicates alternate letters (letters in odd-numbered positions are removed).
'as'+'painter'='aspainter'
The alternating letters of 'aspainter' are 'SANE'.
(Other definitions for sane that I've seen before include "Healthy in mind" , "Free from mental disorder" , "In full possession of mental faculties" , "Sound in mind" , "Compos mentis" .)