Close second slipped catching first person (7)
I believe the answer is:
serried
'close' is the definition.
(thesaurus)
'second slipped catching first person' is the wordplay.
'second' becomes 's' (common abbreviation**).
'slipped' becomes 'erred' ('err' can be a synonym of 'slip').
'catching' is an insertion indicator.
'first person' becomes 'i'.
'erred' enclosing 'i' is 'erried'.
's'+'erried'='SERRIED'
(Other definitions for serried that I've seen before include "Close together in rows" , "(Ranks) in close formation" , "standing close together" , "in packs" , "Rows pressed together, military ranks say" .)