-ну-

The semelfactive suffix -ну- (семельфактивний суфікс) is a specific morphological tool in Ukrainian used to turn a process into a single, instantaneous act.

1. Formation:
It usually replaces the imperfective suffix (like -а- or -и-) of the base verb. For example:

• кричати (to shout) → крикнути (to give a shout)
• стукати (to knock) → стукнути (to knock once)
• махати (to wave) → махнути (to wave once)

2. Consonant Reversion and Simplification:
When the root ends in a palatal consonant like ч, ж, or ш, it typically reverts to the original velar к, г, or х before the -ну- suffix (e.g., кричати → крикнути, дрижати → дригнути, ворушити → ворухнути). This is a reversion of the first palatalization. Additionally, consonant clusters often simplify; for instance, the root блиск- (shine) in блищати simplifies from -скн- to -сн- in the semelfactive блиснути.

3. Consonant Simplification (Dropping of д and т):
When the verb root ends in the dental consonants д or т, these consonants are often dropped before adding the -ну- suffix to simplify pronunciation. For example: кидати (to throw) → кинути (to throw once), шепотіти (to whisper) → шепнути (to whisper once).

4. Stress Shifts:
When forming these verbs, the stress often shifts compared to the imperfective base. While many imperfective verbs have stress on the suffix (кричати), the semelfactive form often pulls the stress back to the root (крикнути) or onto the -ну- suffix itself, which helps in identifying the single-action meaning.

5. Semelfactive vs. Inchoative:
It is important to distinguish between two functions of -ну-:

• Semelfactive: Describes a single, momentary action (e.g., гупнути - to make a thud). These verbs are perfective (they have no present tense and use a simple future) and always keep -ну- in the past tense (він гупнув).
• Inchoative: Describes a gradual change of state (e.g., худнути - to get thin, мерзнути - to freeze). These verbs are imperfective (they have a present tense and a compound future, requiring a prefix to become perfective) and often drop the -ну- in the masculine past tense (він мерз).

6. The Intensive -ону- Suffix:
To add a sense of intensity, roughness, or a casual 'flick' to the action, Ukrainian uses the native suffix -ону- (e.g., рубонути, мазонути). In informal speech, you might also hear the variant -ану- (e.g., рубанути), though this is widely considered a Russianism.