From Wiktionary, the free dictionary
From skemma (“to damage, to spoil”) + -st.
skemmast
- (of objects or items) to be damaged
- (of food) to bad, to spoil, to go bad
Allir tómatarnir skemmdust þannig að við getum ekki búið til salat.- We can't make a salad because all the tomatoes went bad.
