Bear will occasionally roar (4)
I believe the answer is:
bawl
'roar' is the definition.
(bawling is a kind of roaring)
'bear will occasionally' is the wordplay.
'occasionally' indicates alternate letters.
'bear'+'will'='bearwill'
The alternate letters of 'bearwill' are 'BAWL'.
(Other definitions for bawl that I've seen before include "What baby does" , "yell" , "Howl" , "Weep noisily" , "Shout; sounds like dance" .)