Appear to catch sight of a thousand (4)
I believe the answer is:
seem
'appear' is the definition.
(I know that appear can be written as seem)
'catch sight of a thousand' is the wordplay.
'catch sight of' becomes 'see' (I've seen this in another clue).
'a thousand' becomes 'm' (Roman numeral for a thousand).
'see'+'m'='SEEM'
'to' is the link.
(Other definitions for seem that I've seen before include "Appear, look" , "Appear, give impression of being" , "Appear to the eye" , "Come across as" .)