to uprise, to revolt, to struggle
Building blocks
mäss- - rebellion, riot
-ma - infinitive ending
Could be derived from Russian - mešát (to mix up, to bother) or Proto-Finnic - mäsätä (to disturb, to mix up).
In Finnish there is a similar sounding word “mässätä”, which has a very different meaning: to stuff (to eat in a greedy manner).
How to use it
In Estonian both “against someone” and “towards someone” are expressed with the same term: kellegi vastu.
Ma mässan sinu vastu
Literally: “I rebel you against”
Idiomatically: “I rebel against you
Ma tunnen sinu vastu armastust
Literally: “I feel love against you”
Idiomatically: “I feel love towards you”
Examples
Protestijad mässasid politseinike vastu
Literally: “Protesters rebelled police officers against”
Idiomatically: “Protesters rebelled against police officers”
Protestijad - Noun - Gen Pl, "Protesters"
mässasid - Verb - 3P Past Pl, "rebelled"
politseinike - Noun - Gen Pl, "police officers"
vastu - Adverb - "against"
Tuul mässab puude latvades
Literally: “Wind rages tree in tops”
Idiomatically: “Wind is raging in the treetops”
Tuul - Noun - Nom Sg, "Wind"
mässab - Verb - 3P Present Sg, "rages"
puude - Noun - Gen Pl, "tree"
latvades - Noun - Inessive Pl, "in tops"
The word “mässama” can be used when describing weather conditions (torm mässab - the storm is raging, tuul mässab - the wind is raging, lained mässavad - the waves are raging)
Õpilased mässasid eksamiga kolm tundi
Literally: “Students struggled with exam three hours”
Idiomatically: “Students struggled with the exam for three hours”
Õpilased - Noun - Nom Pl, "Students"
mässasid - Verb - 3P Past Pl, "struggled"
eksamiga - Noun - Comitative Sg, "with exam"
kolm - Numeral - Nom Sg, "three"
tundi - Noun - Part Sg, "hours"
Mässama can be used when talking about struggling with something (eg. to struggle with homework - kodutööga mässama)