Lewd in one’s manners — and sort of cross (8)
I believe the answer is:
immodest
'lewd' is the definition.
(thesaurus)
'one's manners and sort of cross' is the wordplay.
'one's' becomes 'I'm' ('one is' is a formal way of saying 'I am').
'manners' becomes 'modes' ('mode' can be a synonym of 'manner').
'and' means one lot of letters go next to another.
'sort of cross' becomes 'T' (resembles a tau cross, a T-shaped cross).
'im'+'modes'+'t'='IMMODEST'
'in' is the link.
(Other definitions for immodest that I've seen before include "Bigheaded" , "Offending against sexual mores in appearance" , "Not humble or decorous" , "Shamelessly indecent" , "Indecent, indecorous" .)