Examine pattern - start with dress (5)
I believe the answer is:
probe
'examine' is the definition.
(I know that examine can be written as probe)
'pattern start with dress' is the wordplay.
'start with' says to take the initial letters.
'dress' becomes 'robe' (robing is a kind of dressing).
The first letter of 'pattern' is 'p'.
'p'+'robe'='PROBE'
(Other definitions for probe that I've seen before include "Investigate closely" , "Question or examine closely" , "sound" , "Inquiry" , "Question or examine thoroughly" .)