Etymology

Cognate with Lithuanian -ininkas (note that -nieks often causes palatalization of the preceding consonant, or even occurs as -inieks, with an initial i that corresponds to the initial i of the Lithuanian suffix; e.g. tirdzinieks) and Proto-Slavic *-nikъ. The feminine form -niece is derived from -nieks with the feminine suffix -e, with palatalization of the final k to c.

Suffix

-nieks, -niece

Added to nouns (or sometimes to adjectives and a few verbs) to form masculine (-nieks) or feminine (-niece) agent nouns, referring to a person whose activity or occupation the original term is (like English -er), or who inhabits the place (city, country, etc.) named by the original term (like English -ian).
Used to nominalize numerals to refer to numbers in the form of nouns (e.g., when speaking of grades, bills (banknotes), when mentioning numbers as labels that identify entities, etc.)