Strange, off and on (5)
I believe the answer is:
outre
'strange' is the definition.
(synonyms)
'off and on' is the wordplay.
'off' becomes 'out'.
'and' means one lot of letters go next to another.
'on' becomes 're' ('on' can be mean 'with reference to').
'out'+'re'='OUTRE'
(Other definitions for outre that I've seen before include "Conspicuously unconventional" , "Extravagant, rather shocking" , "Weird" , "flamboyant" , "Highly unusual" .)