Rigid small bath delivered (8)
I believe the answer is:
stubborn
'rigid' is the definition.
(I've seen this before)
'small bath delivered' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'bath' becomes 'tub' (synonyms).
'delivered' becomes 'born' (as in a baby being delivered).
's'+'tub'+'born'='STUBBORN'
(Other definitions for stubborn that I've seen before include "Obstinate, pig-headed" , "Showing dogged determination" , "Obstinate, mulish" , "Obstinate, bullheaded" , "small boat in Loire, good for going around river" .)