In short

When a suffix bumps three consonants together, Ukrainian usually deletes the middle one — and it deletes it in spelling, not only in speech. From честь comes чесний (no т); from прої́зд comes проїзни́й (no д). This is called спро́щення в гру́пах приголо́сних, “simplification in consonant groups.”

Do not confuse this with the previous lesson. Lesson 38 dropped a vowel (день → дня, the fleeting е disappears). Here a consonant disappears from a cluster. Different sound, same instinct: Ukrainian dislikes a pile-up in the middle of a word and thins it out.

The rule

A word like ра́дість ends in the consonant pair -ст. Add the adjective suffix -н- and you would get радіс-т-н-ий — three consonants с-т-н in a row. Ukrainian drops the middle т and writes ра́дісний. The tongue never pronounces that т, and neither does the pen. (This is where Ukrainian parts ways with Russian, which keeps the letter: радостный, честный. In Ukrainian, write what you say.)

The deletion happens in a fixed set of clusters:

• стн → сн and стл → сл — the т drops (the most common case).
• здн → зн and ждн → жн — the д drops.
• слн → сн — the л drops.
• зкн → зн, скн → сн — the к drops (mostly in verbs from -ск/-зк nouns).

Two everyday words are simplified once and for all in the dictionary: се́рце (from an older сердце — the д is gone) and со́нце (from an older солнце — the л is gone). The buried consonant often resurfaces in a relative: се́рце but серде́чний, се́рденько. Use that cognate to see the missing letter, then delete it in the simplified form.

Beware three groups where the cluster is kept in writing (even if speech blurs it):

• Adjectives from foreign roots in -ст: контра́стний, компо́стний, тури́стський, баластний. The т stays.
• A short memorized list: кістля́вий, пестли́вий, хвастли́вий, хворостня́к, plus the numerals on шість — шістна́дцять, шістдеся́т, шістсо́т, where the т is written and never said.
• The suffix strings -нтств-, -нтськ-: студе́нтство, аге́нтство — т is always retained.

Forms & patterns

Regular simplification (the deleted letter is struck from the spelling):

Lexicalized (fixed in the dictionary; the letter returns only in cognates):

Exceptions — cluster kept in writing:

Examples

Common mistakes

• радістний -> радісний — the т drops in стн → сн (base ра́дість).
• честний -> чесний — same стн → сн cluster; write no т.
• проїздний -> проїзни́й — the д drops in здн → зн (base прої́зд).
• тиждневий -> тижневий — the д drops in ждн → жн (base ти́ждень).
• сердце -> серце — the д is gone, though it comes back in серде́чний.
• солнце -> сонце — that is the Russian shape; Ukrainian has no л here.
• контрасний -> контрастний — foreign root in -ст keeps т in writing (no simplification).
• шіснадцять -> шістна́дцять, шісдесят -> шістдеся́т — т is written even though it is not pronounced.

Tips

• The engine of this lesson deletes a consonant from a three-consonant cluster; lesson 38 deleted a vowel. Ask yourself which one is disappearing.
• Nearly every simplification is written as it is spoken — trust your ear: чесний, радісний, обласний.
• Watch the т first: in стн and стл it drops in almost all native words (радісний, щасливий, якісний).
• To find the missing letter, say the base noun (ра́дість, прої́зд, ти́ждень) — the extra consonant is right there, then strike it from the derivative.
• Foreign-root adjectives in -ст are the big trap: контрастний, туристський, компостний keep т.
• Memorize two short, fixed blocks: the holdout list (кістля́вий, пестли́вий, хвастли́вий, хворостня́к) and the numerals on шість (шістна́дцять, шістдеся́т, шістсо́т).
• Keep т in the strings -нтств- and -нтськ-: студе́нтство, аге́нтство, тури́стський.