This is the 271st most frequent German word.
st
In German, "st" is not a standalone word but a common ending for verbs in the 2nd person singular (du) present-tense form, e.g., "du gehst" (you go).
Here, 'st' is part of the verb 'stiehlt' (to steal), which is a conjugated form of 'stehlen', indicating third person singular in present tense.
Er stiehlt die Schokolade aus dem Schrank.
He steals the chocolate from the cupboard.
In this sentence, 'st' is part of the verb 'bist', which is the second-person singular form of the verb 'sein' (to be).
Du bist ein sehr guter Künstler.
You are a very good artist.
Here, 'St.' is an abbreviation for 'Sankt' (Saint), which is a title used before the names of saints.