What Does This Error Mean?

Kobo dictionary not appearing when you tap a word usually means you are tapping rather than tap-holding — you need to press and hold for about 1 second to select a word and trigger the definition popup. If holding still does not work, the dictionary may not be downloaded for that language.

Affected Models

Kobo Libra 2
Kobo Clara 2E
Kobo Sage
Kobo Elipsa 2E
All Kobo e-reader models

Common Causes

Tap gesture instead of tap-hold — the dictionary requires a press-and-hold to select a word
Dictionary for the book language not installed — Kobo ships with limited pre-installed dictionaries
Dictionary feature disabled in Kobo reading settings
Book is in a language the installed dictionaries do not cover
Tap-hold registered as a page turn on some firmware versions — timing issue

How to Fix It

Use a tap-and-hold gesture on the word.

Touch the word you want to define and hold your finger on it for about 1 second — do not lift your finger until a selection cursor or popup appears. A short tap turns pages or moves the cursor; only a sustained press-and-hold selects text and opens the dictionary. Once the word is highlighted, the definition popup should appear automatically.
Download the correct dictionary for the book language.

Go to Kobo Settings → Reading → Dictionaries. You will see a list of available dictionaries — tap Download next to the language of the book you are reading. Kobo offers free dictionaries for English, French, Spanish, German, and several other languages — all must be downloaded before they can be used.
Set the default dictionary in settings.

In Kobo Settings → Reading → Dictionaries, set your preferred dictionary as the default. If the default is set to a language you do not use, definitions will appear in that language rather than your preferred one. You can also change the active dictionary while reading by tapping the dictionary name in the definition popup.
Confirm the dictionary is enabled for the reading session.

Open a book and tap-hold a word to select it. In the popup menu that appears (with options like Highlight, Look Up, Search), tap Look Up or the dictionary name. If Look Up does not appear in the popup, the dictionary is not installed for that word's language — return to Settings to download it.
Restart the Kobo.

Hold the power button for 5 seconds and select Restart. A firmware bug in some Kobo versions causes the dictionary popup to stop triggering — a restart resolves this temporarily. If the problem recurs after every restart, check for a firmware update in Kobo Settings → Device Information → Check for Updates.

When to Call a Professional

The Kobo dictionary is a core reading feature. If it consistently fails to appear after checking all settings, try a firmware update or contact Kobo support.