Questions & Answers about Он отменил визит.
Отменил is the past tense, masculine singular form of отменить.
That tells you:
- the action happened in the past,
- the subject is one person/thing,
- and the subject is masculine.
So with он, the form отменил matches naturally.
Compare:
- он отменил = he canceled
- она отменила = she canceled
- они отменили = they canceled
This is a question of aspect, which is very important in Russian.
- отменить → perfective
- отменять → imperfective
Он отменил визит uses the perfective verb, so it presents the cancellation as a completed single event.
A rough contrast:
- Он отменил визит = he canceled the visit / he has canceled the visit
- Он отменял визит = he was canceling the visit / he used to cancel the visit / he canceled it at some point in a non-completion-focused way
In most ordinary cases where you mean a specific cancellation that happened, отменил is the natural choice.