Cross including two poles placed crosswise! (10)
I believe the answer is:
transverse
'crosswise' is the definition.
(similar in meaning)
'cross including two poles placed' is the wordplay.
'two poles' can mean two replacements for 'pole'.
'cross' becomes 'traverse' (synonyms).
'including' is an insertion indicator.
'pole' becomes 's' (abbreviation for South, as in South Pole).
'pole' becomes 'n' (abbreviation for North, as in North Pole).
'placed' indicates anagramming the letters (placing the letters).
's'+'n'='sn'
'sn' is an anagram of 'ns'.
'traverse' placed around 'ns' is 'TRANSVERSE'.
(Other definitions for transverse that I've seen before include "Cross" , "Extending across something" , "Crossing" , "Situated across something" , "go in 6 ac [CRISSCROSS]" .)