If you are diving into Serbian grammar, you will quickly notice that some letters love to change shapes. One of the most frequent sound changes is called sibilarization (sibilarizacija, historically also known as druga palatalizacija).

Simply put: When a Serbian noun ends in the consonant -K- in its dictionary form (Nominative case), that -K- changes into a -C- whenever it is followed by the ending -I-.

To be specific, this grammatical shift happens in two specific scenarios:

Masculine Nouns: In the Plural forms for Nominative, Dative, Instrumental, and Locative.

Feminine Nouns: Only in the Dative and Locative singular.

20 Most Common Masculine Nouns with the K to C Shift

The Nominative Singular	The Nominative Plural	The Dative, Instrumental and Locative Plural	The English Translation
učenik	učenici	učenicima	student, pupil
početak	počeci	počecima	beginning
katolik	katolici	katolici, katolicima	catholic
početnik	početnici	početnicima	beginner
jezik	jezici	jezicima	language; tongue;
spomenik	spomenici	spomenicima	monument
praznik	praznici	praznicima	holiday
momak	momci	momcima	guy, boyfriend
pešak	pešaci	pešacima	pedestrian
rudnik	rudnici	rudnicima	mine
poznanik	poznanici	poznanicima	acquaintance
cenovnik	cenovnici	cenovnicima	the price list
predsednik	predsednici	predsednicima	president
zamenik	zamenici	zamenicima	deputy
sveštenik	sveštenici	sveštenicima	priest
vojnik	vojnici	vojnicima	soldier
protivnik	protivnici	protivnicima	opponent
đak	đaci	đacima	pupil, student
vernik	vernici	vernicima	believer
zadatak	zadaci	zadacima	task

20 Most Common Feminine Nouns with the K to C Shift

The Nominative Singular	Locative and Dative Singular	Translation
apoteka	apoteci	pharmacy
biblioteka	biblioteci	library
Amerika	Americi	USA
olovka	olovci	pencil, pen
devojka	devojci	girl, girlfriend
reka	reci	river
muzika	muzici	music
Banjaluka	Banjaluci	Banjaluka
banka	banci	bank
enklitika	enklitici	enclitic
matematika	matematici	mathematics
kritika	kritici	critique
fabrika	fabrici	factory
diskoteka	diskoteci	disco
gramatika	gramatici	grammar
trafika	trafici	newsstand
poruka	poruci	message
logika	logici	logic
unuka	unuci	granddaughter

The Rule-Breakers: When K Refuses to Change

Serbian grammar loves its exceptions! The K to C shift is usually skipped in front of the vowel -I- in two main categories:

1. Hypocoristics (Hyped-up Names & Words of Endearment)

To keep personal and family names easily recognizable, the root consonant does not change:

• baka ➔ baki (grandma)
• tetka ➔ tetki (aunt)
• seka ➔ seki (sister/little sister)
• Žika (male name) ➔ Žiki

2. Hard-to-Pronounce Consonant Clusters

If changing K to C creates a combination of letters that is incredibly awkward or harsh to pronounce, the language preserves the original K:

mačka ➔ mački (cat) — not mačci

tačka ➔ tački (dot/period) — not tačci

kocka ➔ kocki (cube/dice) — not kocci

Grammar Tip for Learners: Don’t stress about memorizing all of these at once! Focus on the most common daily words like poruci (in a message), reci (in a river), or učenici (students).

Want to practice these rules with a native speaker and start speaking Serbian confidently? Fill out our contact form below to book a tailored lesson!

How to know the rule when the consonant K remains K?

Here is a golden rule for this sound change: if the suffix starts with the vowel I, the K changes to C. However, if the suffix starts with any other vowel, the K stays as it is:

K remains K	K turns into C	Examples.
radnik, radnika, radniku, radnikom, radnike	radnici, radnicima	Od najboljeg radnika sam dobila pohvalu. Radnici ne žele novog direktora.
putnik, putnika, putniku, putnikom, putnike,	putnici, putnicima	Agencija je vodila putnike na novu destinaciju. Putnicima se nije svidela nova destinacija.
apoteka, apoteke, apoteku, apotekom, apotekama	apoteci	Beograd ima baš mnogo apoteka. Šta sve možemo da kupimo u apoteci?
devojka, devojke, devojku, devojkom, devojaka, devojkama	devojci	Išao sam sa devojkom na more. Da li si kupio svojoj devojci poklon za Novu godinu?