How can they need reinforcements when they already have half the army directed against a weak, unentrenched Russian wing?
So far as can be seen by aeroplane scouting, this ridge is still unoccupied; certainly it is unentrenched.
1550s, implied in intrenched, from en- (1) "make, put in" + trench. Figurative use is from 1590s. Related: Entrenched; entrenching.