Beginning of joke to do with looking humorous? (7)
I believe the answer is:
jocular
'humorous?' is the definition.
(similar in meaning)
'beginning of joke to do with looking' is the wordplay.
'beginning of' suggests taking the first letters.
'to do with looking' becomes 'ocular' (ocular means related to vision).
The first letter of 'joke' is 'j'.
'j'+'ocular'='JOCULAR'
(Other definitions for jocular that I've seen before include "Given to telling gags (and having fun)" , "With jokes and good humour" , "funny" , "Humorous, joking" , "Humorous or playful" .)