Hunter, or one almost catching one (5)
I believe the answer is:
orion
'hunter' is the definition.
(constellation)
'or one almost catching one' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'catching' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'or'+'one'='orone'
'orone' with its last letter taken away is 'oron'.
'oron' placed around 'i' is 'ORION'.
(Other definitions for orion that I've seen before include "His belt is in the heavens" , "Bright constellation, named after legendary Greek hunter" , "Belted constellation" , "Prominent constellation" , "Constellation - mythological hunter" .)