Two words
May be 2 words combined (retro+murus) If not obvious, probably incorrect
mur.us N 2 1 NOM S M
murus, muri N (2nd) M [XXXAX]
wall, city wall;
retro ADV POS
retro ADV [XXXBX]
backwards, back, to the rear; behind, on the back side; back (time), formerly;
*