One unclear about love language? (5)
I believe the answer is:
idiom
'language?' is the definition.
(I know that idiom is a type of expression)
'one unclear about love' is the wordplay.
'one' becomes 'i' (Roman numeral).
'unclear' becomes 'dim' (I've seen this in another clue).
'about' indicates putting letters inside.
'love' becomes 'o' (love means zero in tennis).
'dim' going around 'o' is 'diom'.
'i'+'diom'='IDIOM'
(Other definitions for idiom that I've seen before include "Expression that's characteristic of particular group" , "Group of words in which the meaning may not be obvious" , "Eg, over the moon" , "Artistic style" , "Language used by group, parlance" .)