Cheers — doctor keeps half of hair gel (4,5)
I believe the answer is:
take shape
'gel' is the definition.
Although both the answer and definition are verbs in their base form, I don't understand how they can define each other.
'cheers doctor keeps half of hair' is the wordplay.
'cheers' becomes 'ta' (both can informally mean thank you).
'doctor' indicates an anagram.
'half of' indicates taking half.
'hair' cut in half is 'ha'.
'keeps'+'ha'='keepsha'
'keepsha' with letters rearranged gives 'keshape'.
'ta'+'keshape'='TAKE SHAPE'
Can you help me to learn more?
(Other definitions for take shape that I've seen before include "Materialise, assume substance" , "Assume a definite form" , "Develop" .)