MEUM+TUUM= a sum

MEUM-TUUM= a difference,

where " a sum" and " a difference" represent 4-letter valid English words making my cryptic uniquely solvable.

The best I' 've got was:

**MEUM+TUUM= UNIT**

MEUM-TUUM= STEE

MEUM-TUUM= STEE

1. SOLVE IT. There is only one solution, satisfying BOTH equations.

2. Try to find better (i.e. less archaic) English words for the sum and the difference of my original quest, leading to a single solution ( not necessarily mine).