Just like one mimicking, say, Renoir in cinema early on (15)

'just' is the definition.
Although both the answer and definition are adjectives, I don't see how one could define the other.

'one mimicking say renoir in cinema early on' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'on' could be 're' ('on' can be mean 'with reference to') and 're' is located in the answer.
This explanation may well be incorrect...

'like' acts as a link.

Can you help me to learn more?