Fool one by one in strike (5)
I believe the answer is:
idiot
'fool' is the definition.
(synonyms)
'one by one in strike' is the wordplay.
'one' becomes 'i' (Roman numeral).
'by' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'strike' becomes 'dot' (I can't justify this - if you can you should believe this answer much more).
'i' inserted within 'dot' is 'diot'.
'i'+'diot'='IDIOT'
Can you help me to learn more?
(Other definitions for idiot that I've seen before include "Moron, fool" , "Foolish character" , "Goose" , "Silly person or dimwit" , "Charlie" .)