Book 1 of the Iliad has the optative form κιχείη. Wikipedia says that ordinarily we expect to see the -η- infix in singular optative forms when the verb is athematic or a contract verb. Neither seems to apply here, so why does this happen here?
I guess the ν in -ανω is a PIE athematic present tense marker, so you could say that κιχάνω is in some sense athematic. But the wiktionary entries for this and other verbs in -ανω don't show endings with η. Is this a Homeric or dialectical thing?
The dictionary entry for κιχάνω is enormous, so check it out for all its various forms. Simply put, the verb has athematic forms.
The relevant part is in Smyth §688:
The following ω-verbs have in poetry (especially in Homer) second aorists of the μι form: ... Epic κιχάνω (ἐκίχην, κιχήω, κιχείη, κιχῆναι and κιχήμεναι, κιχείς and κιχήμενος; properly from κίχημι)
From Beekes:
From a reduplicated root present *κίχημι (like τίθημι), found in κίχημεν, κιχήτην, etc. (ἐκίχεις after ἐτίθεις), which were taken as aorists when the new present κιχάνω arose.
...
The form κιχάνω arose at a recent date after the analogy of φθάνω to ἔφθην, φθήσομαι; the nasal infix in κιγχάνω was modelled on λαμβάνω, etc., on which see Schwyzer: 6885, 698, as well as Chantraine 1942: 300, 392, 415, 446.
