224. The preposition ἀπό means off, away, at a distance from. It is not used adverbially, but is common in tmesis.
Il. 8.108 οὕς ποτʼ ἀπʼ Αἰνείαν ἑλόμην
which I took from Aeneas
In composition it generally gives the verb the notion of separating; e.g. ἀπο-κόπτω is not I hew at a distance, but I separate by hewing; so ἀπεκόσμεον cleared away (Od. 7.232), and similarly ἀποδύω, ἀποβάλλω, ἀπολούω, ἀπορρήγνυμι, ἀποκαπύω (all used in tmesis). Hence we must explain Il. 19.254
ἀπὸ τρίχας ἀρξάμενος
cutting hair as an ἀπαρxή, or first offering
Cp. Od. 3.446, 14.422.
Sometimes ἀπό has the force of restοratiοn or return, as in ἀπο-δίδωμι, ἀπο-νοστέω (cp. ἄψ backwards). So ἀπο-ειπεῖν means either to speak out or to forbid, refuse. In a few cases it has an intensive force, as in ἀπομηνίω, ἀπήχθετο, ἀποθαυμάζω.
With the genitive ἀπό generally expresses motion away from, not implying previous place within the object (whereas ἐξ means proceeding from). It is also used of position.
Il. 8.16 ὅσον οὐρανός ἐστʼ ἀπὸ γαίης
as far as heaven is from earth
Od. 1.49 φίλων ἄπο πήματα πάσχει
suffers woes far from his friends
Il. 1.562 ἀπὸ θυμοῦ μᾶλλον ἐμοὶ ἔσεαι
you will be the more out of favor with me
away from expectation
This genitive is clearly ablatival.