Notice Mike appear (4)
I believe the answer is:
seem
'appear' is the definition.
(I know that appear can be written as seem)
'notice mike' is the wordplay.
'notice' becomes 'see' (notice can mean to spot or see).
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'see'+'m'='SEEM'
(Other definitions for seem that I've seen before include "Appear to the eye" , "Come across as" , "Appear, look" , "Appear, give impression of being" .)