Mother’s absurd dressed in beachwear (7,6)
I believe the answer is:
bermuda shorts
'beachwear' is the definition.
(I've seen this before)
'mother's absurd dressed' is the wordplay.
'dressed' is an anagram indicator ('dress' can mean 'prepare').
'mothers'+'absurd'='mothersabsurd'
'mothersabsurd' with letters rearranged gives 'BERMUDA SHORTS'.
'in' is the link.
(Other definitions for bermuda shorts that I've seen before include "Formal trousers reaching almost to the knee" , "Knee-length garment" , "Attire not quite knee-length" , "beachwear" , "Trousers that end at the knees" .)