Keen to maintain excellent standard up to the midriff (5-4)
I believe the answer is:
waist-deep
'up to the midriff' is the definition.
I can't judge whether this definition defines the answer.
'keen to maintain excellent standard' is the wordplay.
'keen' becomes 'weep' (keen can mean to cry or lament).
'to maintain' is an insertion indicator (maintain can mean to keep or preserve).
'excellent' becomes 'ai' (resembles 'Aw', old-fashioned term for excellent).
'standard' becomes 'std' (abbreviation).
'ai'+'std'='aistd'
'weep' placed around 'aistd' is 'WAIST-DEEP'.
Can you help me to learn more?
(Other definitions for waist-deep that I've seen before include "(Of water) coming halfway up the body" , "(Of water) covering legs and lower body" .)