ictus vs focal seizure

ictus and focal seizure both are nouns.

Word	Noun	Adjective	Verb	Adverb
ictus	Yes	No	No	No
focal seizure	Yes	No	No	No

As nouns, focal seizure is a hyponym of ictus; that is, focal seizure is a word with a more specific, narrower meaning than ictus:

ictus: a sudden occurrence (or recurrence) of a disease
focal seizure: transitory disturbance in motor or sensory function resulting from abnormal cortical activity

Other hyponyms of ictus include convulsion, raptus hemorrhagicus, absence, absence seizure.

ictus (noun)	focal seizure (noun)
a sudden occurrence (or recurrence) of a disease	transitory disturbance in motor or sensory function resulting from abnormal cortical activity