ˀmṣ - to be strong (HALOT 65)

Cf. perhaps (with DRS 23) Arb. ˀmḍ ‘to be strongly resolved’ It is also tempting to compare Akk. emēṣu ‘to be hungry’, assuming the meaning shift “strength” > “hardship, hunger” illustrated by Akk. dannatu ‘hunger’ < dannu ‘hard, strong’