As usual, have answers but cryptic parsing missing...
21a Odd choice (4)
R_R_ must be RARE and hence a double definition. I can see that ODD is a synonym but CHOICE?
18a Dialogue as yet unmentioned in paper, nurturing quality (12)
M_T_E_L_N_S has to be MOTHERLINESS ("nurturing quality") but other than LINES being "Dialogue", I just don't get it